Gateway eMachine T6524
Did that computer come with XP Pro or Windows Media Center Edition ?
Have you tried to reinstall using the recovery CD or the recovery partition ? (on eMachines you need to press F11 at startup)
11.6V is low for the 12V line. See if you can borrow a PSU of higher wattage and test your computer with it.
I see you use AVG. What firewall do you use ?
Are there any red or yellow devices in the device manager (start => run => devmgmt.msc) ?