It can also never hurt to have more RAM
...
RAM helps everything! (sometimes...) and also another reason could be is that you are using an undedicated video card. If that is true and the video card is attached to your motherboard it means it is sharing RAM and using unwanted power (plus it is prob a crappy one that dell put in there) You can buy a new PCI video card (make sure your computer has a PCI slot) for really cheap...
2 Gigs of Ram = $50 - 60
an okish video card $100-200
Also try using programs like CCleaner, Defraggler and a-squared (free edition)
http://www.ccleaner.com/download
http://www.defraggler.com/
http://www.emsisoft.com/en/software/free/
Hope this helps or I might just be talking too much.
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