Black screen with blinking underscore after clean

[garion]

Hi, I have been having a problem where my computer would just turn itself off, this happened about 6 times, so I decided to search it and see what it might be, the first thing I saw was over heating and all I need to do was clean the inside, so I took it apart wiped it down inside with a cloth wiped the dust off the 2 fans I knew how to remove the one in power supply and the one that's at the back of my desktop, now when I start it, it goes to the startup page then to black screen with blinking underscore and goes no further, I had a new motherboard fitted about a week ago due to overclocking frying it. please help me

 

[Cycloid Torus]

Can it POST? Can you get to BIOS? Is that stable? What are temperatures in 'health' section of BIOS?

Please review http://www.computerhope.com/issues/ch000607.htm