Question : Problem: won't post

I have a emachine t6420 that won't post. When I turn the power on, the cpu fan starts but after about 10-15 seconds it stops. I have already switched power supplies.

Answer : Problem: won't post

Been down this road with quite a few customer machines.  Every one of them, all eMachines, had bad mobo's.  And, in some cases, the mobo blow wiped out the CPU.  eMachines almost always uses PSU's that are undersized, regularly starving the mobo for power, eating the caps.  Replace the mobo.