I just had to trouble shoot a friends HP laptop, because she said she had a Grey main screen upon looking at this, I found that the home screen is still working so are the programs but you can't see them for the grey screen also, the computer is "Working in the background as indicated by the spining icon, I check task to see if any abberant programs might be involved everything is as should be (or should I say as windows wants things to be.) Current trouble shooting, took the battery out,pulled the power supply will leave unpowered for 24 he's to drain all power and try to restart the PC tomorrow. Has anyone ever run up against such a problem before? And how were they able to resolve this issue.
Look and see if the fluorescent lamp in the back of the display is on. If not, the bulb or the inverter has failed. EDIT: What is the model number of the laptop?
Try booting into the bios and see if the screen works from there, if not then connect the laptop to a pc monitor. If it works with a monitor connected then it could be the lamp (most likely) or possibly the screen inverter. When you connect the pc monitor and it's still grey or blank then it is most likely the video GPU and that may mean a new motherboard