Mp laptop has a blank screen only mouse

Try restarting and wait at least 5 minutes to see if the screen appears, if not reboot and run in safe mode and see if you get the same problem, if you don't then your best option is to perform a system restore.

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

this is a software issue, conflict in software or drivers, came up with similar issue on a Lenovo laptop, came up with blue screen error messages after hanging up. First temporary solution to avoid hanging during start up, allow computer to finish the system start up until it finishes with the desktop displays with out doing any keyboard or mouse activities until you see at the bottom of the screen or on the task bar that the internet connection has been established. Pressing keyboard keys or mouse buttons causes the system to hang up. If it still fails , run MIcrosoft Fixme software to determine the software at fault so it can be removed or repaired.

The blue screen (BSOD) is usually caused by a new piece of hardware or driver. But there is a code on the screen which will give you more information about the problem. Put the code into a websearch site and the possible cause should be given.

Good Moring,
I have seen this behaviour in computers with virus (maleware) you can try the following
1)start your antivirus while log in safe mode and run a full scan
if virus is found remove it and start windows normally run a full scan afterwards
2) if no antivirus is install, i would recomend you to reinstall the OS

try restoring this unit to an earlier time
in restore function is a calandar check which things were updated last time

go to start
all programs
accessories
system tools
restore

heres the restore function

Run your install disc and re-install the OS.

Do you have the original recovery disk? I recommend inserting the recover disk, restart the computer while continually pressing F12. Select boot from CD, press any key when asked, and you would want to do a "repair". That should fix your problem. 

ok my friend as you said the operating system is not loading any more so that means we are having some corrupt files that makes the windows to fail while trying to boot up.

and since you cannot even log in to the computer even in safe mode that means you have only two options.

first is to try a repair (most of the computers use F12 key to get to the repair counsel).
second reinstalling windows.

so try the first one if it doesn't work then reinstalling windows will be the last thing to do.

if you need and further help please let me know

cheers