I am running a Compaq Presario, 160 gb hd, 512mb of ram and is about 6 years old. I am running Windows XP Home Edition. I have about 107 gb used space. I think I am running SP2

At random times, the computer will restart without notice. After it reboots an error message states " The system has recovered from a serious error."

These are the two files that have been causeing the problem but I cannot find them and don't know what to do with them even if I do... :(

C:\DOCUME~1\Owner\LOCALS~1\Temp\WER4e1f.dir00\Mini 090508-03.dmp
C:\DOCUME~1\Owner\LOCALS~1\Temp\WER4e1f.dir00\sysd ata.xml

I understand that 1 is a dump file.

Some times my PC will keep booting up after the home screen comes up. Sometimes it just restarts once.

I have tried to update to SP3 but half way through the install process, it says Access is denied.

At one point, I also got the BSoD.

I do not know if I have a virus but I would appreciate if someone would help me... :D

The problem like this can be caused by so many things that it can be difficult to nail down.

You've mentioned one thing I always look at first: viruses and spyware. Make sure that your anti-virus software is running and is being updated regularly, that should happen daily.
It could be any new software or hardware, if the problems started happening after installation. Depending on the software or hardware, my first reaction would be to look to the vendor for reported problems and possible updates. In particular, device drivers are the most likely to cause crashes and reboots without warning.
You should still make sure that your system is up to date including drivers for new hardware.

If your computer has been running fine for some time, and you haven't installed any new hardware or software recently, then look at your fans. The fans are often the first to fail either due to accumulated dust and dirt or simply age. When the fan stops working, the machine overheats, and when the machine overheats it can crash. (Randomly)
The next most common problem is a failing power supply. If you've added more hardware to your system over time, you may simply be demanding more of the power supply than it was designed to provide. Power supplies can fail slowly, meaning that they can become marginal before they fail completely. And the symptoms of a marginal power supply are random crashes. Replacing the power supply or having someone replace it for you is often an inexpensive test.

Six computer years is about 600 adult years give or take a little exaggerating. Before spending any money fixing it you should look at a new machine.

Computers age around ten to fifteen years for every calendar year.
It's said a computer of five years old is still useful but approaching retirement.
Like Moore's law there is no mathematical foundation; it is simply a rule of thumb. (Like dog years)

Thanks a lot Blakecory, I have updates my NVidia Geforce Video Card and I have used these following anti virus/malware cleaners.

AVG Anti-Virus Free
Malwarebytes
Ad-Aware
Stinger my McAfee
Windows Defender
Windows Virus Removal Tool
CCleaner
Defraggler

I have checked my fans and they seem to be running o.k I have to ask a simple question also though... I have 2 fans, 1 which is at the heatsink, and the other an output fan behind the CPU. Should there be one at the power supply? I have been using Speed Fan and my Temp1 temperature has gone to 142 degrees F! I do not understand your computer year terms all that well though... Is my computer becoming old for a 6 year old computer. I do not know how I can solve my problem yet but these are some of the drivers I have downloaded...

NVidia update
Part of SP3
Security Updates