Posted 29 July 2009 - 12:14 PM
Of the two possibilities I can think of, Hamluis has suggested the first. The power supply. As electronics get older, especially inside of power supplies, they tend to not "output" enough voltage or amperage to get everything going.
With that being said, the other thing I would look at would be the hard drive. You stated that the hard drive is making a "little noise" but works fine.
Hard drives are also an electronic part but they are also "mechanical". Mechanical in the fact that they "spin platters" internally and are spun by a motor with bearings. As these bearings get older and start to "dry out" ( meaning the lubrication levels are not as if they were new ) they tend to be harder to startup thus causing power issues. After powering on and off multiple times, it is possible to "jump start" or "jolt" the drive into spinning at the proper speed internally and have your pc up and running at almost normal speed and condition.
I would recommend first backing up your computer and then running the manufacturers ( hard drive manufacturers ) testing utility against your hard drive and see what it says.
My gut feeling is that you have a hard drive that is about to "lockup" and no longer boot for you but I could also be very far from the mark.
Hope this helps,
"Admire those who attempt great things, even though they fail."