Similar problems were caused by bad RAM. It passed the boot check OK but was not compatible with the MB/Processor (bought them together, both good brands). Try another RAM slot, DDR should go in slot 1, but maybe it will work in another slot anyway.
Clean the contacts with a pencil eraser, then compressed air to clean it and the slots.
When you have had enough problems and fixed them, you could get a job as a computer repair guy!