I have a 7 year old computer I let my 5 year old boy use. When I updated my main computer recently, I tried to put some of the replaced parts into his computer (motherboard/cpu/memory/videocard - everything but the hard drive). When it was all complete, it wasn't booting up. I reset the cmos and tried again. Still wouldn't work. I decided to format his hard drive and reinstall Windows. Windows would get to about 10% on the files saved and would then keep saying it couldn't install files x y and z. So I thought it might be a bad hard drive and replaced it. Installing windows on the new hard drive gives the same error. Any thoughts?

clean the CD your installing from first..then if still no go check CD in another system to make sure it's ok..... Good Luck

So far I tried installing it on a cd-rom and dvd-rom installed on the computer. Also, the CD itself is very clean, no scratches. I also borrowed a friend's copy and get the same results. When saving files it gets to 8-10% and then says it can't save xxx file (its usually a different file each time).

Check the capacitors on the motherboard. Look at the link below to get an idea what they are. http://www.computing.net/answers/ha...

I presume when you say "it wasn't booting up" you mean it wouldn't boot into windows but would boot up into BIOS. That is to be expected since windows was installed in a completely different hardware environment and it is not easily migrated. In most cases a repair instal will rectify the situation but you've already gone beyond that by formatting the drive. Your installing problem isn't related to the boot failure. Most often these type errors "unable to copy file xxxxx" are the result of faulty or incompatible ram. Since you say you took the motherboard, CPU and ram from your old box to put in this one then incompatibility shouldn't be an issue. Download Memtest86. There is a version that creates a bootable floppy drive or an ISO file you can burn to make a bootable CD. Boot up with Memtest and let is run at least one full pass. If you have more than one stick of ram, run the test on each stick separately ( Remove the other stick) then reinsert all sticks and run the test again. It is just possible there is a bad contact happening in the ram slots. Cleaning the contacts on the sticks using a pencil eraser can sometimes help. Aother possibility would be to leave in only one stick of ram during the install process and reinsert the other stick/s after windows has been installed. Goin' Fishin' (Some day)

yeah check the RAM - i had trouble installing Windows once before and tried plenty of different solutions. The only thing that ended up working was throwing away my Patriot RAM and installing Kingston.

"The only thing that ended up working was throwing away my Patriot RAM and installing Kingston" I hope you didn't mean that literally?