Puter reboots on it’s own

I have 3 comuters on a home network (4 port router)one computer started re-starting itself all of a sudden. Thought we had a virus….re-formated the hard drive after removing the battery because system would not boot at all after awhile. (only beeped continually)

Did this twice and formated drive “c” three times to ensure not just a low-level format process…

Back to re-starting itself and now justs beeps continuously. Could this be a virus in the CMOS or in the boot sector of the hard drive?

What should I do? How will I know for sure what the problem is? Should I replace the battery first and go from there? (I know – too many questions)

please help!

thanks