Dead notebooks with no symptom describing what you recently did, and error/freezes/crashes before hand and such are near impossible to diagnose.
As always I recommend taking out the notebook drive and hooking it up to another computer throuch IDE adapter or usb case to pull all critical data/applications/application activation keys. Backup before anything else.
Now if you have warranty coverage and certain that you did not spill anything if you do not have the additional $$$ accidental warranty coverage then its a good time to excercise it and see how good it is.
If you do not then.....
The only thing I can recommend for diagnosing for the home user when no further info is provided other than dead machine is to
1) remove as much equipiment as possible (i.e. no external devices plugged in, out of the port replicator, removal of one of the two memory chips, removal of PCI and mini PCI cards, and removal of any modem/network cards that might be accessible and then try a reboot.
2) Parts swapping and using known good parts in your machine and using your parts in other know good machines. For instance if you notebook Hard drive works when hooked up to another machine when you back up data then it probably is ok though I would use a chkdsk, Defrag, and a utility to check the SMART parameters to see if anything shows as a problem and also listen to hear if the drive is excessively loud (a whir or clicking way in excess of what you remember). You can also use utilities to pull off the Event viewer from the HD to see if it says anything, this is a bit more involved and requires a system with a nonWindows OS or utility that allows you to do this and probably a bit more than you can do easily
Also some parts swapping you can try yourself, like using your machine with just one memory module installed then the other. And also swapping what socket they are in. You can also try a external monitor plugged in though you will have to remember to use the keypad to cycle to external monitor.
Also you can try boot discs in your CD, like even just your windows restore cd, to see if it will boot.
If you can get ahold of another Notebook drive to swap and try out that would be very helpful since so many problems are assoicated with hard drive failure from everyday use especially if you use it in your lap or while traveling or on an unstable surface where it bounces around alot. You do not need a working OS on the hard drive, just a freshly formatted drive will work for swapping and diagnosing to see if it boots.
Also try to go into BIOS when you first boot up.
There are alot of parts on a notebook that can come loose. Try pulling them out then reseating them. Some of the most common are the Hard drive connection and the video card to LCD cable.
I recommend just going methodically through this process as much as you can. I would caution though on having it repaired. If you do then get in writing a estimate, and also ask about the costly diagnosis fee. Many a time the cost of repair can not be justified compared to the price of buying a similar working system used and even in some instances where you would do better buying new.
It might be a good time to ask for some help from the computer geek friend you have that might have a few notebooks around and can swap parts. Also if you no someone with the same model that can really help on proprietary/custom parts like the video card.