Try setting your alarm for 9 or 10am and then get up no matter how many hours sleep you have had. Do not nap or anything through the day and go to bed at maybe about 9 or 10pm.
If you are finding you cant sleep untill 7am do a bit of exercise or housework or something during the day to try and tire urself out and go to bed at a reasonable time, even if you are lying awake for a few hours. If you are waking up, dont get out of bed just try and get back to sleep.
Theres no easy way of getting out of this pattern, you are going to have to have a few days of tiredness.
If you say you cant stay up for 24hrs without falling asleep, dont give urself the opportunity to, stay active, dont lie down, have lots of caffine!