Help!!! sony vaio pcg-792L

Hello,
I have a sony vaio pcg-792L with Windows XP. I started having trouble with the boot up and kept getting a blue error screen. it then began to give me the following error code: Windows could not start because the following file is missing or corrupt <Windows root>\system 32\ntoskrnl.exe. please reinstall a copy of the above file.
Now I get the initial vaio startup page and then it goes to a black screen. sometimes I get a cursor before it goes to the black screen. none of the buttons work. when I do press buttons upon start up it freezes at the vaio screen or doesn't even get that far. The computer did not come with a windows disk, but I do have a windows xp disk. my computer will not even boot the disk, no matter what I do. I appreciate any suggestions.