Why won't my laptop stay on?

a few days ago my laptop stopped working. it turns off after about ten seconds. there is always a beep right before it turns off. originally i had windows xp but about six months ago a friend changed it to windows 7. it worked cine for about a month. after that it told me it was not an original program and gave me a warning ever time i started it but it still worked perfect... till a few days ago. once it staid on long enough to see a quick message that said something about changs in the program or something of the like. i have my original recovery disk for my laptop. a friend told me that if i reset it it would be fine. but the computer won't stay on long enough to run it. is the problem do to the improper upload of windows 7 and if so, how can i fix it. thank you all for your time.