CPU and Posting

[Soarinex]

So I have a old dell optiplex that I've been using for simple browsing and I soon realized it had the wrong processor in it. I replaced the pentium 4 with the core 2 duo and the system refuses to post and I've taken it down to the barebones of hardware and used a newer pentium 4 reset and updated the bios and I don't understand what else I can do. Putting the original processor that the system came with out of the factory doesn't work only the old pentium the fans spin and an amber light comes on and it runs forever 

[Soarinex]

I have yet to find why when I put any compatible CPU into the motherboard with the latest bios version it doesn't post. I've reset the cmos battery wiped the bios and even put a different make of the same processor in the slot and it refuses to post unless I use the original CPU that was in it.

[Dango]

POST issue:

1. Check CPU and Motherboard power cable, make sure they are install correctly.
2. Check CPU and RAMs, make sure they are all the way in.
3. Check BIOS make sure you install it correctly.
4. Look for debug LED or Code and check with your motherboard manual

[WkdPaul]

Threads merged and moved to the troubleshooting section.