From my experience with computers over the years, I've determined there are a few things that can cause this to happen (hanging at the BIOS).
• IDE Misconfiguration -- This wont apply if the machine has SATA -- I dont know Compaq's that much, so I dont know how "new" this model is. This can, however, stop the POST in it's tracks.
• Dead CMOS Battery -- In my experience most motherboards will contine to boot at normal speed even with a dead battery. However, when unplugged the machine will fail to remember the time and any BIOS settings.
• Loose/Halfway-Plugged-In connections. -- This is especially true for IDE.
• Fans -- Although I've not had this problem myself, but I have read that some motherboards will not continue to boot if it does not detect that the CPU fan is spinning (the 3rd wire on a fan is for speed control and/or RPM monitoring).
EDIT: Forgot the most important one.
• Memory - Faulty or incompatible RAM will also stop the boot process at the BIOS screen, typically with an error, however.
Might want to check those. I suppose you could try resetting the BIOS settings by taking out the battery, and leaving the machine unplugged for .. About 5 minutes or so, and put the battery back in and plug it in.