Computer will not start-dead motherboard?

Have you check to see if the power supply works just because you see the light on the motherboard that does not necessarily mean that it is working.

To test if it will power on unplug power supply from wall then unplug all power supply cables from the motherboard and all drives except one cdrom drive then on the 24pin motherboard connector get a paper clip and put the paper clip in pin 14 which will be a green wire its the only green wire on the connector then put the other side of paper clip in any of the black pins on that same connector this will act like a switch it will not hurt power supply. If it is function properly it will turn on and the fans will start running

CPUs are very hard to kill I doubt its the CPU most likely its the power supply dells are notorious for having cheap power supplies.

The usual suspect is the PSU.

Our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...