Laptop Black Screen and random restart

hi

having trouble with my laptop which is only 6 months old (so still under warranty)
started off by randomly crashing them bluescreening continuously. this was fixed after phoning my supplier who got me to change a setting in the bios (ahcp was enabled instead of disabled). this then solved the problem and got it on again.

however i now have a new problem! a few times the screen has gone completely black (similar to standby) but there is nothing i can do to get it going again so i end up turning it off by holding the power button. it has happened after hours of using the laptop and at varying different times between that and turning it on.

tonight it also randomly restarted itself after being used for about an hour then when it had juta loaded windows the screen went black and i had to reboot.

does anyone have any suggestions? i have run scans for viruses spyware and ran a scandisk check a few days ago. i have recently changed antivirus after having problem with them.

Any suggestions would be greatfully received