missing drive c

Clarifications

1 system, or multiple systems?

I think maybe your company should invest in some UPS's, and power strips, and new power supplies if multiples.
Otherwise, it may just be that the HDD needs to be replaced, or the PS needs to be replaced, or even Windows needs re-installation. Well, also can be a memory issue or MB issue.

Please post with more details

I think that this could happen if you are running short on disk space on the Hard Drive. Windows likes to have at least 15%-17% free space on all drives for it to function properly. If you are below this limit it is effecting the Operating Systems ability to function properly, try moving some of the files to a central repository {storage area} on the Network or to an External Hard Drive..UBCD will allow you to burn to CD if you can't access Safe Mode. http://www.ubcd4win.com/downloads.htm

Try deleting all the temp files on the system by booting into Safe Mode with Networking to access a Central Store and running Disk Cleanup to remove all Temporary files. Empty the Recycle Bin, also you should have access to USB for Storage.

You may also have to do a System Restore to get the PC to function again.

Keep us informed as to your progress if you require further assistance.

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