Power Supply, Graphic Card and CPU Problem ?

450W is a good average PSU for a good average office computer, but as you increase the demands, you're going to have some trouble. I would definitely suggest in getting a new power supply. If you have a computer case with a permanent power supply, then you're going to have to get a new case. Look for a case that either has no power supply (and just buy the PSU seperately), or one that has at least 550W to be safe.