Custom Computer - Vista Not Start

Hello,

Recently My Custom computer has not been able to start up at first it would run for a few moments then shutdown this reminded me instantly about when I was first building this computer and the Heatsink fan wasn't attached correctly and it would overheat. expecting that I re-applied Thermal Compound to the CPU and Heat sink and tried laching it back to the mobo. This is where I discovered that the HeatSink's prongs wouldn't hold onto the CPU tight enough which I plan to fix or replace sooner or later at the moment holding the fan down agianst the CPU keeps it down to a good temprature and keep s the comp running. And now Vista isnt starting up not in safe mode or anything it loads the files then gives me a black screen with just my mouse. After reading some of the other topics on this forum I decided to Boot from the Vista install disc. Success! then it wouldnt proceed past the login screen but sadly the login stuff wasn't popping up just the background. Im at teh end of my rope with this already I need help. This is my first build and Im not sure what else to do! Posting this from my dad's work laptop.