We have replaced our power source and installed new harddrive and programs. Seems to have a issue with the communication/connection to the monitor. It has always seemed to be gone into sleep mode (amber light) and then wouldn't come back on, had to power off with button and restart. Did the above work as diagnoised as possible problem. But computer still wasn't turning on consistantly. Now won't go into windows at all. How can we determine if it's a bad video card (as now also suggested) or what?