My best guess would be that a RAM module is defective, try and take all the ram out and put one RAM module in, if it boots up and goes to windows then shut down your PC, take out the module and insert another module and continue doing this until the problem happens again and then you know what RAM module is defective.However if your pc doesn't boot with any of the RAM, Then the ram isn't the problem but at least you can cross that of the list,
Good luck