Guys my PC has shutdown and when i switch it on it shows a blue screen telling me that the computer has shut itself down.what can I do to fix this problem?

Get it repaired? Either you have a hardware problem keeping the system from booting, or there is a software problem with the operating system. I would suggest trying to boot into the BIOS - hold down the F2 key when you power it up. If that doesn't work, then it is likely a hardware problem with the system. If it does work, then your hard drive may be failing, or your operating system has become corrupted.

For Hardware issue, you can run the diagonise test, to detect faulty in hardware.
If diagonise if fine, then you can reinstall the operating system.