It really could be anything and its pretty hard to tell from just a description although overheating does jump out at me. It seems your pc has more than enough raw specs, so thats not the problem.
Have you checked to see if you have the latest version of your bios? Often this can fix a number of errors.
Also, it could be anything from as the above poster mentioned, cooling problems, is your computer clean and well ventilated? To bad memory, to viruses/spyware etc.
My advice to you would be to:
1) go to dell support downloads and make sure you have the latest version of their bios for your computer as i suspect that you don't
2) go to windowsupdate.microsoft.com/ and update all available updates, reboot, revisit windowsupdate.microsoft.com/ and make sure you have everything (this is very important)
3)clean your computer, make sure the fans inside of your pc are working, and make sure your pc is in a well ventilated area.
4) Take the above posters advice, make sure your memory are connected properly, and run a memory test to make sure your memory sticks are both still good.
5) Run a full online antivirus scan with kaspersky antivirus,
www.kaspersky.com/virusscanner post the results here
6) Run a fully updated (important!) spybot search and destroy scan
7) Run hijackthis and post your log here, and i and others will check your log and make sure nothing looks wrong or out of place that may be causing these problems.
If you do all of that, im almost positive we will be able to , if not eliminate the problem, at least identify it and give you steps to fix it. Let me know how it goes, good luck.