For the last two weeks my computer has been not wanting to turn on . When I hit the power button it won't let the computer boot up to vista. Sometimes it works and sometimes it doesn't.

I am a certified PC technician and from my experience this is most likely a power supply issue it's usually about thirty dollars for the power supply plus labor it's not a difficult repair but is one you will want a technician to look at as most power supply units carry about half the power of the electric chair I would advise you not turn it on as this could harm the other internal devices (the power supply is failing and is not giving proper voltage to the motherboard, cpu and ram therefore sometimes it gets enough to boot windows and sometimes cuts out earlier than that) pc's run on direct current not ac they need to stay with in .3 volts of their rated power consumption you are either overloading or sagging power (too low) that's all I got :) good luck