Systems Lock up overnight.

It's possible that they are set up to run scheduled maintenance tasks every night, and failing (though that wouldn't explain the 95 box).

Check under Accessories, System Tools for scheduled tasks and turn of if they are enabled.

Is it the same ones locking up? Win95 is known to hang after 45 days, and in that case, all of them will now hang and then be ok for another month or so and you'll go through all this again.

Heat? Do you turn off the AC at night? Does it get too warm?

Are these 8 machines on a different power circuit -- is anything else taking power or causing power fluctuations on that circuit? (i.e. cleaning crew's vacuum cleaner, etc.)

Have you updated your virus protection and scanned recently?

Those are what come to mind. Good luck!
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GET RID OF THE DELLS!! hehe.. sorry just had to say that. It is not uncommon at all for Windows 98 and Win95 to lock up over a certain period of time. Mine at home does the same thing from time to time. All though I must admitt, they dont do it everynight. All I can say is make sure you read what the 2 gents before me posted. Then you also might want to try going into cmoss. There are also power settings in there you might want to play around with.

Since you have disable the the power management in the BIOS and power management in Windows, I assume that the machines are not getting enough power to run them overnight. Try checking the power requirements for the machines and make sure there is enough juice to run all the machines. Either that or the Unix server is taking up all the power. Not only that the operating system maybe unstable, making it sometimes unstable to run overnight. I have ecountered the problem before and it occurs randomly with different machines making it difficult to solve.

You could be having a windows memory problem if these PCs are all configured the same. You've probably done this, but make sure no screen savers are running when you leave for the day. Plus, try opening system monitor and running it all night to see what is displayed at the time of lockup. Make double sure no screen saver is enabled so that the screen can be viewed in the morning. This trick has worked for me in the past with funky problems like this.

When I've had weird, spuratic lockups like this, I've been somewhat successful by removing programs that are loading at startup. Remove anything that may be in the tray that is not absolutely necessary. Check for programs in the "Startup" folder, autoexec.bat, the "Run" or "Load" statements of the Win.ini and even the "RUN" key in the registry.

Hope this helps some.