HDD detection

Hello. Posted this several weeks back but sidetracked with other issues and never did get it resolved. Now I'm back to this PC to give it another shot.
Got a Compaq Deskpro EN that I installed W2K on. On cold reboots, I get a message about no fixed disk present. I hit F1 to continue, then a message about finding the HDD and the type of HDD. I hit F1 to continue and no prob; W2K will boot right up and machine is fine. On restarts, it is fine. If I shut it down and boot back up within a few minutes, it boots up fine. If I let it sit overnight, turn it on, the above mentioned problem occurs. I've been in CMOS/BIOS, can't find any setting about detection HDD.
Help!!!??? :confused:

THANKS!

I believe your cmos battery may be failing.....the autodetect hdd should be in the first section of your bios....your cmos battery is about the size of a nickel and can be had at any local computer shop.

CMOS/Bios battery and what some of them look like.