How to stop my computer terminating over and over again?

My computer has pms and every time I turn the computer on, a little pop up appears that tells me I have approximately 45 seconds to save everything before 'the system terminates' or all will be lost. The only way to get around this, I have found, is to beat the countdown and restart from the start menu. Otherwise, it will restart itself repeatedly, non stop. This clearly isn't normal. Why is this happening? How can I make it go away? Any help would be greatly appreciated.