im looking at buying an imac g5 on ebay, and the guy says "As of a couple of months ago, computer started acting up. I believe the issue is the logic board/heat, but have not had it looked at professionally or in an Apple Store. The computer will power on for about 20-25 minutes initially, then each time the machine powers off, the time is shorter. Everything has been erased off the hard drive, and returned to original settings.", does anyone know whats wrong with it? so i dont buy it and end up not being able to fix it