Hi, I have a 24 inch early 2009 3.06 mhz iMac computer and it has been having very serious hardware issues. The computer was repaired twice. The 1st repair, Apple sent an in-home technician to replace the power supply and the 2nd repair, the technician replaced the logic board, harddrive, power supply and a power cable. Three days after the 2nd repair, the computer started to shut down randomly and any external drive connected to the iMac via the usb port, would immediately cause the iMac to shut down. I would like to add that these were the issues that resulted in my having the 2nd repair done. By the way, I've also tested all the five external devices that I used on my iMac and inserted them onto the usb ports of my Macbook Air notebook and they work perfectly. Does anyone have any suggestions as to what could be causing these issues? Thanks!