msdos.sys gone

[F525]

Good evening all,
A friend called for help with his W95B system. It would only boot up to a C: prompt after a brief flash of the windows Splash logo.
Turns out that his MSDOS.sys file was gone.
Typed C:\Attrib msdos.sys and the file wasn't there to remove the hidden property.

I restored the file from another machine and that fixed the problem.
* But why did this happen?

After it was running again, I did a full virus scan... no virus's.
I ran Revival undelete utility... there was no "#sdos.sys" file on the hard drive. Like it vanished into thin air.
Anybody have this happen before? or ideas what might have caused it?

Thanks,
Dwight

[Tim M]

1. Have you performed a scandisk? Maybe the sector where it was has gone bad.

2. What AV program did you use and are the .dat files current?

[F525]

Hi Tim,

Yes, I did a scandisk from DOS right away. It found no errors. I had to use the dos version, because I was not able to launch windows at that point.

I also tried the backup copy of the dat files (system.da0 and user.da0) i.e. renamed them back to system.dat and user.dat, to see if that would work to load windows. No luck there.

Finally saw that the msdos.sys file was missing. Loaded in a copy from my own machine, and that did the trick.

At that point, since I didn't know what AV he had or how current it was, I went to http://www.antivirus.com and if you hunt around a bit, there is an "online" disc scan they call "House call" which will scan your hard drive for you with the latest AV definition files, for free. It takes an hour or so with a dial up, but it works good.
Thanks for your thoughts.