You could tell what OS, but type in AUMHA SHUTDOWN at google.com to find the usual shutdown troubleshooting guide. Sorry I can't be more specific but you didn't tell what OS.
I have a Sony Vaio PCG-GRZ610, known problem with their shutdown,(through other forums).
it turns on, the disk is spinning and that's it, sometimes it comes up all the way to the desktop, i can go online and perform regular tasks, but after sometime shuts down automatically without any notice, and wont boot up again, i dont know what seems to be the problem
please help, still got to pay the remainder of the loan.