This sounds to me like a hard drive clutter problem. I’ve known the Norton programs to create “cruft” on a hard drive, so it’s possible you haven’t been taking very good care of your hard drive.
(0) Back up your most critical data to CD or DVD. Do this first, as you may not get another chance. The troubleshooting steps I’m going to suggest are hard-disk intensive, and might cause a borderline drive to fail.
(1) Boot your computer in safe mode and open a command window (“cmd” at the “START>Run…” menu). Type chkdsk c: /f to run a disk check with the “fix errors” option on. WinXP occasionally insists on doing this immediately after a reboot; if prompted to do so, reboot. This may take up to 30 minutes on an 80GB drive, especially if there are other undiagnosed problems.
(2) From the “START>Run…” menu, type defrag c:. This will defragment your hard drive. You can also use the Windows-based defrag utility, usually located in Accessories > System Tools > Disk Defragmenter. It gives a graphical display of progress which can be more comforting than the blank black DOS prompt. The report that pops up at the end of this routine should tell you a little bit about the state of your drive before and after the defrag. If your drive is more than 75% full, this can take a long damn time. I just defragged 12GB of data on a 60GB drive, and it took about 35 minutes. When you read the concluding report, note carefully if your page file and/or MFT have become fragmented – a fragmented MFT can lead to an inoperative OS, and can only be repaired with 3d-party software (like Executive Software’s “Diskeeper”, made by the same people who wrote DEFRAG for Microsoft).
(3) Try a 3d-party utility to read the SMART status of your hard drive. I used this one once, but I’m sure there are better ones, and free ones, available with a quick Google.
On preview, leandroc76 raises a good point, although I’ve always heard the rule of thumb as 15A on the 12V rail. It might be useful (for our purposes) for you to open your case and get the serial number of your motherboard, graphics card, and power supply. Most other components draw either insignificant or model-invariant amounts of power.