It is most likely a hard disk error. This could be caused by dust, old age or any number of factors. The first thing you should do is unplug the computer, open the case and then check the IDE and Power cables to make sure they are properly connected.
If they are connected, look over the hard disk for dust, do not directly try and remove it, but if you can blow on the hard disk to get rid of some of the dust do so.
After you've made sure it's all hooked up try a few startups (about 10 or 12) and if you can get it booted up once back up everything
. I know someone who had a similar problem, and got the hard disk to boot up once and put everything on disk, afterwards it wouldn't work again.
If none of the above works, I suggest you buy a new hard disk (put an operating system on it) and put it in the computer as the master, and your old hard disk as the slave. It is possible for old broken hard disks to work as long as they are only the slave drive (not advisable as a permanent arrangement as it obviously won't work as a slave for long, but hopefully enough time to salvage any data).
Once you are sure you have all data off your old hard disk, it's probably best to format it. It may give it a few years extra life, but be sure to make sure you have all data you want off the hard disk before you format.
Originally posted by welshboy222
I agree 4 years for a hard drive is hard work
My dad's old computer had a 128mb hard disk that was bought in 1992, and was worked hard, and still works. But 4 years heavy use may cause a hard disk to not work.