Probably worth testing your memory . . click on the link to Memtest in my signature . . let it run on one stick at a time overnite or until it starts reporting errors
How to burn an ISO file: http://www.techsupportforum.com/f149/how-to-burn-a-bootable-iso-file-341778.html
What Model is this Dell?
What Operating System did it come with?
Do you have the Reinstallation disc that came with it?