I still cannot boot XP. When booting from cd rom, I get the following message:- A problem has been detected and windows has been shut down to prevent damage to your computer etc., and suggests running CHKDSK /F ? Please see previous message 138541. Any suggestions please?

This is just one of many possiblilites. Run memtest sounds like bad RAM

You might want to remove the HDD from that PC and slave it into another and then run chkdsk on it. You might also want to download and run (while it's still slaved) an HDD diagnostic utility. Check the HDD manufacturer's web site for such a tool. If they don't have one, try Hitachi's "Drive Fitness Test".

I have no clue what's been tried already... and I just posted this try in another post so I'll just copy and paste the same info... let us know if this helps.. Couple of things to try: 1) Try hitting F8 before the "loading windows" screen appears, this should bring up a menu of choices. Try the "last good config" option and see if that works. The "safe mode" option is a good second choice. if that doesn't help... Insert your XP CD and boot from the CD, let it run its checks, then do "repair", this should bring up the recovery console. Once there it will ask you what windows to log into (probably only one, so enter "1")... then enter your admin password (if you don't have one or can't remember, just hit enter). Once at this point, type this without the "" marks: chkdsk /r there's a space after K and before / TK.