Desktop not starting

Hello, DJ..

Iam using Wipro desktop.
Till yesterday night everything is fine...
But today morning onwards it is not booting up...
But fans and hard disk are working..
I tried removing RAM, cleaning it replaced in another slot, nothing worked...
But after holding the power button for 5 seconds, it is shutting down( probably all fans are spinning off)...
Then what might be the reason for not starting...
I am not a member in this forum...
I hope you understands the problem...