Power led blinking, no signal!

Hello,

I an encountering some problems with my gaming computer. Last night, i was playing BattleField Bad Company 2 on the pc and i saw that it was lagging, so i decided to clean up the GPU card as i havent clean it at all since a few months. I unplugged all the cables and started my cleaning. then i wondered that the pc would run faster if i clean the ram too.
I removed the 3 GB ram (2GB:Stronium memory, 1GB Kingston memory)
after cleaning them i put them back. Booted the PC and no signal, i automatically thought that i havent put the ram well but the problem persisted. I removed the additional 1Gb rama and booted the pc with 2 gigs only. the pc booted , i saw tge bios screen on startup, windows loaded up and i could surf on the web. but i was looking for a way to make the 1GB more ram work on my pc. so i turned it off and placed the 3rd ram(just to see if i have luck, seems not) but now when i pressed the button, there is a no signal message and the power led blinks. i saw on this forum that holding the power button, unpluging the power chord and pluging the power chord again would work, and now the pc starts but the light stopped blinkling. please note that all the fans work, processor, psu, case fan.

if someone can help me on this, here are my specs






Any help is kindly apreciated .

thank you