Try running the Dell diagnostics if you still have them. Other wise, try a Live CD which has things like memtest86, there's some more specialised ones.

There's also at IBM Developer Works is a "Linux hardware Stability" guide written by Daniel Robbins, worth a look to.

What operating system is giving you the trouble? If xp then try system restore. Have you downloaded anything new that may account for the trouble? If it is xp can you get an xp disc to use so you can use fixmbr to repair the Mbr. How many applications do you have running when it freezes? How much ram have you got and what type of CPU and graphics card are you using?

Linux will freeze if you are running too many apps at once. How big is your linux-swap partition? If you don't have a swap partition and you have low ram then you will see a lot of freeze ups. If it totally freezes you can re-start X by hitting Ctrl/Alt/Backspace. That will restart x without a total reboot. Being sure that you have the correct video driver will help too. What type of video card do you have? How much ram?

Linux should not freeze if you run out of VM, there's an OOM (Out Of Memory) killer which will actually terminate processes.

If the machine "freezes up" then it won't accept keyboard input, so how is CNTRL-ALT-BackSpace going to work?