Laptop Screen goes blank

Try this link, looks like you need to repair boot:
http://h30434.www3.hp.com/t5/Notebook-Lockups-Freezes-Hangs/HP-G72-b66US-Notebook-PC-Dosn-t-Boot-into-Windows/m-p/1336579#M22150

When the screen turns on does it show anything or does it turn on and go to black?

If it goes to straight black it could be two things typically.
1. The LCD screen is having an issue. Connection cable / LCD screen itself.
2. The Graphics Card has gone out.

this requires screen replacement. Its similar to stuck pixles but is caused by the controller board on the lcd. replacement of the cable will not fix this either.

Sounds like your GPU (graphics processing unit) is going out.

If you don't see anything at all and it has not been dropped or banged it maybe something as simple as the Video out selection. Look at the keyboard and locate the [FN] and the [F4](Actually look for the key with a small video screen on it which is usually the F4 on HP machines). After turning the computer on press and hold the [FN] key then press the [F4] Key. There are 3 modes programmed into the video selection. Computer monitor, Computer monitor and External Display and External Display only. What happens a lot of the time is someone may have accidentally pressed this combination of keys and the video is actually redirected to the external monitor only option. If this does not help and you can connect the computer to an external monitor and use that key combination to get the output to that screen then the problem is most likely the Back light for the monitor of the screen itself. Both can be replaced. HP can provide the back light part at a reasonable price. For the screen itself I recommend you go to someplace like E-Bay and purchase the replacement. Make sure you look at the sellers past record so you don't get taken. I DO NOT recommend using Craig's List for anything.

it will be ok if you reinstall your os

windows or you need a bios reset

screen FL inverter get faulty change it

I assume that when you dont use your computer you put it in a sleep mode by pressing sleep button ..so if this is the problem you are facing than there is nothing wrong with your video card and solution for this problem is that remove both the power cables and also remove the battery for time being, after some time put back your battery in the laptop and plug the power cable and restart your laptop it will work fine...........
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What is the exact model for your laptop? If you go to HP website using the laptop, you can have them "autodetect" what drivers you are actually supposed to be using. Find the display driver associated with your specific laptop and use that. Look for the link to "Software and Downloads" and click on it. There will be a black button in the middle for "Autodetect". Download that latest driver.