Push start up button - cpu fan spins on & off

Hello,

My desktop just wont startup any more.

When I push the start button, the cpu fan starts and stops over and over - but the computer never boots up.?

I had tried to check on why I had lost one of the 4 g memory ram card ( used to have 8 g) - but absentmindedly I inserted one of the chips 180 degrees backwards. When I tried to startup the fan just kept on spinning - so after correcting the flipped ram chip - the above problem shows up.

Any help will be greatly appreciated.