My new laptop was locking up- so I did a herd reboot. Green lights, but no screen...several tries later removed battery and restarted. Now it has a DOS looking screen that demands a password- any ideas other than "password"?
I agree with saugen send it in and let them sort it out for you. That's what the warranty is for.
I remember reading here some time ago that this could be the symptom of a dying hard drive. If the laptop is out of warranty, try attaching the hard drive to another computer and run some HDD diagnostics programs on it. There are plenty of free ones out there. I like Drive fitness test, but I don't recall if it sees USB drives or not, so you might have to mount the HDD in a desktop.