i cannot boot my macbook pro and any key combination is not working it only showing a gret screen

Oh shoot ! -this is the Mac Pro forum, not MacBook Pro. That being said: I’ll try to help you, at least a bit. See if you can reset the smc/pmu, then zap pram.how to do that can be found on apple’s support page for notebooks, or if you can’t wait like me-google or yahoo. If that does something good, then try rebooting from the Recovery Partition ( command + r keys held down on reboot until it reboots) then go up to top middle of screen, and run OSX Tools, then Disk utility. Assuming it all checks out, set your startup disk, then proceed. If not try reinstalling the OS. I’m sure someone else will post here & help you out if I couldn’t....

John B