|PLEASE quote the EXACT error you're getting, and check what you type after you type it, and try not to make typos.|
Apparently, you can't edit the first post in a thread on this site after there is a second post in the thread (a string of posts), but you can edit any of your own posts after the first one.
IF AND ONLY IF you were quoting the right one, it's:
The computer restarted unexpectedly or encountered an unexpected error. Windows installation cannot proceed. To install windows , Click "OK" to restart the computer, and then restart the installation.
Are you SURE you quoted the right message?
Did you write it down, or are you guessing this is the right message from what you remember?
When I search with that exact message (without quotes around it) on the web, there are LOTS of "hits" for Vista and Windows server 2008, but NOT for XP! It appears to be a Vista and Windows Server 2008 ONLY error message, and a LOT of people are getting it. Some are installing XP because they haven't been able to figure out what causes it!
There are similar messages for XP, but they are NOT the same as you quoted.
According to this, your model you list above either comes with Vista 32 bit or XP Pro.
HP Compaq 6720s Notebook PC - specifications and warranty
Did yours come with XP Pro, or did you load some XP version on it from a regular CD after getting fed up with Vista, or are you trying to replace Vista with some XP version ?
If you actually have Vista on your computer, or if you are trying to install XP to replace the Vista that is on your computer but that has not been deleted yet, say so!
General t-shooting stuff.
Unplug everything that is not necessary to run Windows Setup when you run Setup.
If you have changed any BIOS settings, go into the BIOS Setup and restore the defaults. You need to press a key while booting in order to get into the bios Setup.
In the case of more recent HPs and Compaqs that's often F2 - the key you press may be stated on the screen while booting - if not, the key you press is stated in your user manual for the model.
Usually repeatedly tapping the key while booting works the best - do not hold it down - you often hear a beep each time you tap the key once the bios is already entering or has entered the bios Setup.
Disable any timers that make the laptop shut down or go into standby mode after a certain amount of idle time. Windows usually manages these settings but sometimes they can be found in the BIOS as well.
Has this computer EVER worked?
(In some cases, a new brand name system computer with Vista on it gets this error the first time you attempt to use it!)
If it has....
What was the computer doing before, or what was(were) the problem(s) before, you tried to install, or re-install, Windows??
The specs say your model could have come with as little as 512mb of ram installed. You state you have 1gb, but is that what this computer had originally?
Have you changed which ram you have installed since the computer last worked normally?
If you HAVE, you may have installed ram that is not 100% compatible with the main chipset on the mboard, or on recent mboards, not compatible with the memory controller built into the cpu. If you still have the same ram that was in it before when it worked fine, try installing just that ram.
If you changed the ram and DO NOT still have the original ram, test the ram (or in any case, you could test it).
If you have been fiddling with the ram, or if someone has for you, or if you have dropped the laptop or could have possibly jarred it physically otherwise, do this BEFORE you test the ram:
See response 2 in this - try cleaning the contacts on the ram modules, and making sure the modules are properly seated:
For a laptop, you must remove both its main battery and AC adapter before you do that.
If there is a user manual for your model on the HP web site, or a Maintenance manual for your model (there is usually both), you could look at that/those for further info about installing and removing your ram, if you need to.
If you want to try a memory diagnostic utility that takes a lot less time to run a full pass than memtest86 does, this one is pretty good - Microsoft's
Windows Memory Diagnostic:
It can be toggled (press T) to do a standard or a more comprehensive set of tests - use the default 6 test one first - if it passes one pass of that, use the latter one. A few of the tests in the latter set are intentionally slower (they disable the cache on the cpu).
If you don't have a floppy drive, see the Quick Start Information at that Microsoft link for how to make a bootable CD of the Windows Memory Diagnostic (you need Windiag.iso - you don't necessarily need to use the program they mention to add it to the CD).
Are you trying to install Windows from a regular Windows CD, or from a burned copy of a Windows CD, or from a Recovery disk that came with the computer, or from a burned Recovery disk you made in Windows using the built in HP/Compaq program?
A burned copy of a bootable operating system disk should be on a CD-R or a DVD-R for the greatest probability it will be read properly, and must be made using "disk at once" or similar in the burning software - the file that makes the disk bootable is normally invisible even if your OS and program is set to show hidden and system files, so if you merely copy the contents of the disk that you can see, the disk will not be bootable. A CD-RW or DVD-RW disk or other type of burnable disk may not read properly in a drive it was not made in (unless it's the same model).
If you are trying to install XP to replace the Vista that is on your computer but Vista has not been deleted yet, DO NOT try installing XP from Vista - boot the computer using the regular Windows CD or a copy of one, and DELETE the existing partitio
ns if you don't want Vista anymore.
Similarly, if you want to re-install XP from scratch, you should not try running XP Setup from XP, or from some other operating system, in most cases.
If you want to try Repairing the existing XP installation, without deleting the contents of the partition Windows XP is on, you must boot using the XP CD, and choose to Repair it the SECOND time you are asked. If you want more details about that - many call it a Repair install - let us know.
When you boot the computer using a bootable disk (CD or DVD), you should see a message early while booting "Press any key to boot from CD" or similar - if you see that, press the stated key before the text disappears (often, within 5 seconds of when it first appears). (If you are using a crt monitor, it may not be warmed up enough at that point for you see the message - you may need to boot again to see that.)
If you DO NOT see that message, if you have only one optical drive, the boot order settings in your bios Setup are not set right so that you can boot from a bootable CD. Go into the bios Setup and change the boot order such that a CD drive is before any hard drive (and/or SCSI) in the boot order - it does NOT have to be first in the boot order - it just has to be before any hard drive - if you ever use a floppy drive, a floppy drive show be before a CD drive in the boot order - otherwise, a bootable floppy in the floppy drive may not be recognized while booting the computer.
OR - sometimes, on brand name systems there is a specific key or key combo you can press while booting to change which source you boot the computer from - you may see a message while booting regarding that.
If you have two or more optical (CD or DVD) drives installed, many bioses will only boot a bootable disk from the first one of them it recognizes while booting - in that case try placing the bootable disk in the other drive if you don't see the message and the boot order settings are correct.
If you actually have Vista on your computer, and want to fix it, I found lots of other suggestions on the web.