Now what's wrong???

It's not just for AMDs and such, you'd be surprised how low some of the power supplies can be, especially in cheaper computers (such as those with celerons)...

 

Wow, too many cooks can spoil the soup. Back up anything important to floppy's etc..
Reformat.
if your puter manufacturer used a partition of your harddrive to rely on to reinstall windows, contact them and get the CD discs that were suposed to be suplied with your computer. Use those to reload whatever version of windows you had.

 

Oh, and tell whoever else uses your comp to surf for porn that you installed netnanny.

 

She can't format it if she doesn't have her Windows CD as she stated already.

I say back up important stuff just incase it doesn't boot one day.

Other then that this is a hard one to tech via the net. Doesn't sound like the powersupply for a few reasons.

A) winamp won't keep a power supply from failing... and you said if you keep winamp running it won't reboot.
B) You don't have a lot of peripheral devices plugged in sucking extra power
C) its an older comp so I'm guessing the video card is not extremely demanding in the power supply department.

You can't fdisk and format it because you don't have the windows 98 install disk. And also if you have never done that procedure I wouldn't recommend doing it on your own without guidance unless you don't mind the possibility of getting help if you can't make it work or just junking it...

If no new RAM was added, then I doubt the RAM (or lack thereof) is causing it to restart.

Overheating could be a possibility -- although MOST motherboards will give you a system "BEEP BEEP BEEP BEEP" as it is restarting as a basic motherboard error. One reason it could be overheating is if the fan inside is not working.

Does it do the same thing if you boot it into safe mode? Have you tried booting into safe mode?

Safe mode will disable any drivers and software not necessary to run the basic operating system. if it works fine in safe mode then you know its a software issue and you can take it from there.

Sounds like you have more than one issue though. I'm betting if you can do CHKDSK and Defragment the hard drive that will speed things up a bit -- but probably not help with the rebooting problem.

If the computer is really that old you may want to consider purchasing a new one.

Keep us updated!

To get into safe mode you can use F8 (i am pretty sure it is F8 on win98)

 

keep in mind that formating isnt always the best bet. dispite your aged hardware there are some things you can do to make your computer a bit quicker.
some more suggestions:
if your computer has gotten a slower than it was before there are a few things to keep in mind. with the more software you install the slower it gets, regardless of how many times you defrag to arange the data on the platters, the more there is the slower its accessed. but 9 out of 10 times its spyware and viri, i would suggest getting a good spyware remover (spy sweeper, or dare i say.. microsoft's spyware remover) to start, and end as many processes as possable in task manager and good scan of your pc. while your ending those processes if you notice any with an iffy name that keep poping back up after you end them chances are you pc is infected with a virus as well. now if you have done all of the above and it still seems sluggish while booting you might want ro run regedit and look in HKEY_LOCAL_MACHINE/SOFTWARE/MICROSOFT/Windows/CurrentVersion/Run and delete entrys for crap like real audio and stuff that you really dont need loading when your computer boots. that always seems to speed loading the GUI up noticably. best of luck..