Compaq Presario 5000, WinMe, 64 Mb ram, 17.6 HDD
Loses the hard drive.
When the computer is booted, no operating system found....
go into the bios, bios informs that new drives have been found;
F10 and the computer is up and running.
CMOS battery seems ok - date & time are being kept
What could cause the bios to loose the hard drive?

Just to clarify:

Are you saying in order to boot into ME you need to manually go thru the BIOS setup?

Then it boots ok?

jephree, no, the bios losses the drive indiscriminately.
Once set in the bios, it works fine until it doesn't want to, then it needs to be rest.

Have you opened the computer and made sure all the connections were good?

Unplug/ Replug ...

Does this happen often?

Haven't checked the internal components --> will do.
regarding happening often - no only happened when the customer returned from a holiday

First thing i would check is the harddisk
Grab a Windows 98/ME startdisk from http://www.bootdisk.com
and boot from it. Then check with FDISK that the partition information is in order