PC refuses to boot up...

[=CrAzYG33K=]

This is what happened ..

My board is a Twin board (ie. supports both DDR and DDR2 RAM)
My comp was running perfectly fine on DDR2 RAM.
Then wanted to try DDR . Didn't boot. Now changed back to DDR2 and still no boot

Thing is fan rotates ...
But the keyboard's 3 Lights don't come up.. and the Monitor doesn't have any input .. No display ..
I've tried everything .. clearing CMOS, removing battery et all. But to no avail

I've had this same problem with two other comps..
Is it because of change in memory frequency?

I'm sure lots would have faced this same problem before.
How do I solve it?

[patkim]

Do you receive any POST Beeps from internal speaker/buzzer after you power on the PC?
Very preliminary thing you can try is ensure that there's no dust on the memory and other slots on the mobo. Just do a basic cleaning and see if it boots with minimal devices connected to it i.e. just one memory stick, onboard VGA etc.
Dust could cause the system to fail to detect components and it may not boot, especially if it is opened and altered after many months.

[ravi_9793]

There must be some beeps sound at start Up..please count them.

[=CrAzYG33K=]

^ You're assuming it's a memory issue?

[Batistabomb]

Originally Posted by =CrAzYG33K=

^ You're assuming it's a memory issue?

DEFINETLY , this was RAM issue,majority of display problems are only because of graphics cards or RAM , count the beeps