I've had this problem for a long time. The problem is that my xbox powers on very seldom. Sometimes it tries to load the dashboard but then the red ring starts flashing and the screen gives error code 7(refers to HDD error). Sometimes absolutely nothing happens when I press the power button. Usually i eventually get to the dashboard just by trying to boot it MANY times. Could the problem be power supply? I don't think that it's the harddrive because when I get the xbox to start normally, it reads and writes everything flwalessly. I have checked the cable connections and removed all the dust and dirt from it. Any ideas? More info: I've had the console in my closet for almost a year. Last week I tried to start it and it booted correctly on the 1st try. Now couple days later I try to start it again and nothing happens when I press the power on -button. It "tries" to start for about a second (I can hear a very quiet sound within it) then it stops.
It's hard modded. I have unplugged HD and DVD and it still doesn't start. So I guess the problem is PSU, MB or mod-chip.
