We have an older Dell Optiplex GX620 with a P4 chip. It runs great, except, whenever is is shut down it loses its drivers. I mean the mouse, audio, microphone, on and on. When it reboots it will just sit there until we can trick it into getting an Internet connection and then it will automatically download a host of drivers. of course none of them are "Microsoft Approved" so one must approve every installation of every driver.
It always keeps perfect time so do not think it is the CMOS battery, although we replace that just in case. No affect.
Running XP SP3 and dedicated to a couple of old programs that are important to us.