Question : Problem: MOBO BAD? NO BOOT 2 BEEPS 1-2-3 LIGHTS NO MONITOR MONITOR LIGHT REMAINS AMBER

Did I fry the MOBO or corrupt BIOS? I installed a new HDD in my Dell Dimension 9100.  I tried to enter BIOS to enable it - tapping F1,F2,ESC,DEL,F12, etc.  The Dell logo never appeared before Windows XP SP2 started.  I never got into BIOS.  It would boot but not recognize the new HDD.  I updated the BIOS but still unable to access.  I tried to clear/reset the BIOS by removing the CMOS battery for 30 minutes.  I put the old battery back in, put the power cord back, and fired up the computer.  The keyboard light came on, the light on the monitor remained amber (it usually turns green right away), and, the diagnostic lights stopped at 1-2-3 with a 2 beep burst.  Did I fry the MOBO?  Dell's analysis of the light is ambiguous: A 1-2-3 sequence means "Another failure has occurred."  I tried re-booting w/o the new HDD.  I tried again after reseating the original HDD cables (which were untouched), removing and reseating all the cards and cables - no luck.

Thanks in advance.

FWIW: the diagnostic lights in sequence as follows:1-4; 3-4; 2-4; 1-2-3;3-4;1-4;2-3-4; 2-3;1-2-3;3;(2 beeps); 1-2-3

Dell's diagnostic lights analysis: http://support2.jp.dell.com/docs/systems/dim9100/En/SM/adtshoot.htm

Answer : Problem: MOBO BAD? NO BOOT 2 BEEPS 1-2-3 LIGHTS NO MONITOR MONITOR LIGHT REMAINS AMBER

If it wouldn't boot from a basic system, hard disk nor any other drive is the problem. It's narrowed down to video card, memory, motherboard, and CPU.

Motherboard failure is more common than CPU failure. This one is difficult to call and I wouldn't rule out the CPU. Do you by any chance have access to a POST card? Any other video cards or memory you can swap?