I'm new to the forum and I need help. I have an old Dell Optiplex GX150. When I turn on the machine the Dell logo appears and posts but Windows won't boot up. After a minute or so the logo goes off and I get the following message:"Press F1 to try again or F2 to enter setup. I've tried F1 to no avail and when I go to F2 there doesn't seem to be any help there. What next?