For the first system I suggest checking both RAM and hard drive.

Download Memtest+ v1.70 from the link midway down this page . If you need a burning program to create an ISO image on CD then try Alex Feinman's ISORecorder . Note that there are different versions for XP SP1 and XP SP2.

Boot up from the CD, floppy or flash drive and let memtest run through 3 or 4 complete tests (preferably leave it overnight). This will find any failings in your RAM.

To check out the hard drive, download the diagnostics from the manufacturer's website and save to floppy or CD. Boot from the disk you made and run the full suite of tests (the quick tests will not tell you anything meaningful).

Have you installed the drivers for the CD drive on the other system? What Operating System is this running? How old is the system?

sorry for the late reply i tryed editing my post but wouldnt let me , anyway i got the first one fixed already and the 2nd one is also fixed and incase your wonder the one that had the cdrom problem has a 233mhz P2 but everything is good now and i will soon be moving on to my 6th and 7th computers lol, yes i have a bunch and so far all of the ones i have fixed have 128megs of ram and windows xp

Just curious - what are you using these systems for? 8.4GB disks ar small for a system running modern software, and 128MB RAM is, as far as I'm aware, the bare minimum for running XP.

And I would guess the cost of the OS is more than what you would get if you sell them on.