Maybe just maybe your cooling fan has gone out and the computer is shutting down to protect itself.

First advice - if you need to ask, repair is probably beyond you. And with only "funny noise" to go on, it's hard to know where to start. Nothing appears on screen means the system is not even beginning to run - problem with power supply/motherboard/ram/video card/monitor - most of the computer! Before doing anything inside the case, remember computer components are static-sensitive and even a small shock you can't feel can be enough to destroy computer components. See http://www.kitchentablecomputers.com/static.htm I start to analyze problems by removing everything inessential - hard drives, CD, Floppy, plug-in cards (except video), check the wiring and look for anything floating around loose within the case. Then turn on and see what happens. Remember hard drives are easy to damage and must never be dropped or knocked hard - treat it like blown glass and it will be ok. If you have a helpful friend (or second computer), first check your monitor by using it on another PC. If that works... The first thing to replace is the power supply. It's easy and relatively cheap to replace, and if the power supply is bad, it can destroy whatever is plugged into it. So you don't want to start by replacing the motherboard! If the PSU doesn't help, you;'d need to work through the other options - as you can imagine this can get expensive if you don't have a pile of spare parts lying around. Depending on the configuration of your PC, it might be more cost-effective just to replace it.