I have a Hp with win 98 and after i log in it shows" the file C:\explorer is not a vaild MS-DOS program it may be damage' But if I go thur the C: and type cd\windows enter and win it will boot up

I've seen the problem in the past, what I do is to re-install to repair it. But.. I would also try to copy the system files from a A: (Win98 boot disk) back to your C drive. Something like this in DOS: A:\ copy sys C:\ Obviously your Windows directory is there, just something messed up in the boot area. There is a few files Windows 98 look for upon boot, so check those. I don't remember on top of my head, it's been awhile. Something like: Command.com, IO.Sys, Config.sys, Autoexe.bat, etc.

the comamnd in A:\ prompt is "sys c:" and not "copy sys c:"

If you can get into Windows, extract Explorer.exe from W98CD into C:\Windows. Also, look to see if Explorer.exe is in C:\Windows, and also in C:\. To be on the safe side, would download the 30 day evaluation copy of Trojan Hunter (http://www.misec.net/) and install it, then run Trojan Hunter and see what it reports.