Thanks guys for all your input.
I'll try and explain it in a little more detail without confusing the situation.
BIOS picks up the 40gig drive ok. I then initialized the drive in Disk Management, then formatted using NTFS. This was my D:\ drive. My DVD/CDROM is my E:\ drive.
This configuration worked for sometime. The problem seems to happen when I disconnect the CDROM to "temporarily" connect a 3rd harddisk for data transfer etc.
ok, get rid of 3rd drive, reconnect CDROM, bootup, and my d:\ drive is knackered. XP thinks its the 3rd drive, partition info, volume label, size etc.