So I have had this old windows vista desktop computer for a while and just recently when I turned it off the next morning it wouldnt turn back on until 4 days later. now 1 week later i turned it off again and i havent been able to turn it on for a month. wont make a noise there is only a green light on the back of the computer.

Are you willing to risk a dollar? Try a new CMOS battery. And tell more about make, model and age.

You sure that there are no power problems? Also specifications would be good to know, as it is quite tough to give a thorough solution on something. AS there are so many different configurations. Hopefully, after 2 weeks OP still decides to do something about his issue.