Hi Everything was fine until yesterday on my comp (Win XP SP3). I temporarily copied a lot of data from an Ext. HDD onto my C drive. I even got the 'low disk space on C...' message. I had a lot of work to do so I kept on working without freeing up space (dont know if the low space is related to the probelm). After a while I started getting random popup messages along the lines of The instruction at "0x00000" referenced memory at "0x000000". The memory could not be "written". Click OK to terminate. Click Cancel to debug. OK and Cancel buttons Every program started showing these messages. IE would not open etc. Even opening Windows Explorer was giving the same message, although I was able to see and work with Word and Excel files in C: drive. So I decided to restart the computer and move the files out of C to freeup space. But now the computer wont restart! It boots normally (although I dont hear the startup hardware beep but dont know if I've ever heard the beep), the Windows XP splash screen appears and then I can even see my custom wallpaper but the desktop (icons and taskbar) does NOT load. It starts giving me the same error messages (The Instruction at "0x000...) for all programs userinit.exe, svchost.exe, etc. At this stage, Ctr+Alt+Del brings up the Task Manager, I can restart and shut down successfully but comes back to the same place (wallpaper loads but not desktop with Instruction at "0x00 errors). Safe Mode also brings back the same error messages and desktop wont load so I cant try Sys Restore either. I thought a Windows repair might help so I put the Windows XP install CD into the CD drive (the same disk used to install the OS successfully with same hardware config) and it says press any key to boot from CD. I do, it says something like 'Setup is detecting your computer's configuration....' then after 2 seconds it just goes blank. The keyboards NumLock is still on but the monitor has just blanked. Just stuck with this - I have important data on C: and the last backup was 3 weeks back... Any help would be greatly appreciated

Yes, because your computer does not have enough Physical RAM to run all of your programs so it is using Hard Drive Space which you have none. Either upgrade the memory or try these steps. Ctrl+Alt+Del -> Task Manager -> Click File -> Click New Task -> Type Explorer.exe Now Click Start -> My Computer -> C: Drive and remove the stuff that is taking up too much space. Also try Right Clicking C: drive and do Properties and hit the Disk Cleanup button which will remove tempory files and deleted files in your recycle bin.

Thanks ace omega. You may be right about the space. But I cant use any of those options. When I try to run any new task in Task Manager, it shows up those same error messages (The instruction at "0x00000" referenced...) again. So how do I get into the drive to be able to delete data?

Plenty of physical ram if the posted 4gig is correct. Next step is to go in under Recovery Console. Start by running chkdsk /p What you describe has all the signs of malware/virus activity

wanderer, yes it is 2x2048 RAMs. As I mentioned the cmd prompt itself wont open (even in safe mode). Any ideas?

Your going to have to boot like Wonderer said from you Windows CD in repair mode to get access to your drive. This is looking more and more like a Virus. I would get an external drive or slave a second drive in and backup all of my important files and do a system recovery.

Since this happened after a massive copy I suspect the boot files are beyond the 1024 mark and as such can't be read to be booted. Since you can't access the drive via recovery console [you may have had to add hard drive and video drivers] my suggestion is get a knoppix boot cd and use it to leach off your files, clean up disk space and then see if you can boot. BTW if the disk is completely full I don't believe windows can boot since it needs to write temp files to do so.