Have a problem with PC. When I switch on the screen comes to life with message at bottom(press enter key to interrupt boot)tried that after a few attempts for PC to start without success. After a few seconds Windows xp show's on screen. Then Welcome. 15 seconds later screen saver shows on screen & box makes fan noise. Then goes back to Windows xp on screen & whole cycle starts over again. Originally it did just one try & box switched off. Is it worth fixing or am I better buying a new one.