Here’s a picture of my Dell Latitude D630 when it boots up.
The random freeze started around 2 days ago. Out of sudden the laptop will freeze, and left the screen with a blue’ish tint. A power cycle is required to get the computer back to work, and it happened a couple of times a day. Last night when I was working on my talk for this Sunday on it, it just dropped dead and refuse to turn back on. The symptom looks like there’s something wrong with the video card (it would sometimes boot with two Dell logos in “split screen”).
Anyway. It’s my work computer so it’s covered by warranty — but the Dell guys won’t be able to come and fix it until next week. Meanwhile I am stuck computer-less. :(

I thought you use.. Mac :P ???
This is a known problem with Dell D630.
http://en.community.dell.com/blogs/direct2dell/archive/2008/09/12/nvidia-gpu-update-limited-warranty-enhancement-details.aspx
I have the same laptop which has the same issues. Unlucky for me I bought mine at an auction and Dell simply refuses to do anything about it. :(
Try to get basic tests – memory, disk drives (point your attention to S.M.A.R.T. parameter “heads recalibrating”) and internal/CPU temperature.