MacBook Keeps Locking up

Hey guys I'm sorry if this is somewhere else and or if it turns out to be a software problem . So i have a 2007 White MacBook and when i tryed to restart it it just ended up giving me a blue screen with the color wheel spinning and it stays there . so i toke out the hard drive and checked it with my macbook pro and it said the hard drive had failed so i got a new hard drive and installed mac osx on it and got it back in my white mac book and it was ok for a couple of hours and then it just froze up and when it restarted it want get pasted the grey sceen with the apple and none of the boot keys ( C T or Shift and even the Options key) work and i can see anything else that would be the prob other then the logic board please help cause if it can be fixed without spending a lot of money it would be nice

Have a look here and if those steps dont provide any hope it might be Genius Bar or cert repairer.