It might help to have a bit more background information as to whether this just happened on it's own or if you were in the process of doing a download, installation, etc. Since it is a laptop I assume the same issue occurs on A/C power or battery, also what OS are you running, again a bit more information may help.
I have an Acer Extensa 4420-5239 that now won't boot up. I turn on the computer, the screen stays blank. I see the power light turn green, it tries to run, but after about a minute it shuts itself off. I removed the hard drive and reseated it to see if that would help -- no dice. Is it dead?