System does not allow me to logon

[ultra]

hi
I was using 2000 pro for a while now. but suddenly I started getting the error message about the some files being modified. so I installed XP after reformatting the harddrive. It was successful and I could use the XP for some time. but I got the same error message again and again
'some files are modified with unknown versions, insert the windows xp cd....'
I did that, but it was doing nothing but repeating the error message. So i thouhgt it was because of Xp. So I reformated my system again and installed the 2000 pro . it worked fine until I got the same message. I tried to do exactly what the message says by inserting the 2000 Pro CD. but no change.
now the system is not allowing me to logon and giving me the error message
\System32\ntoskrnl.exe is missing or corrupt.
I could reinstall the 2000 pro, but why is this happening again and again? is it because Virus?
Thanks
Ultra

[bailey]

are all these O/S cd you have the orignal or working copies of the orignal.

sounds like something is corrupt in the file system or maybe you got a virus on a floppy your useing, or even in the bios

I am betting eather you cd are bad copy's
or you got a virous that you keep putting back on some how