According to your description, the computer halts during Power On Self Test (POST); that is the significance of your observation of the white progress bar when you first turn on the power. It is often caused by a poor connection to one of several different components, the hard drive, the CD ROM drive, and occasionally, the memory modules. To improve the connection you should unplug the cables one at a time, followed by immediately reconnecting them. This action wipes the oxidation from the pins to improve the connection. The same thing can be done with the memory modules by using the levers at each end of the module. To re-insert the memory, place a thumb at each end of the module (never in the middle of the module) and press until the levers move up and re-latch the modules.
Given that the problems occur during POST, it is not possible that the problem was caused by Windows 7. At the point you are seeing this failure, Windows 7 has not begun to load.
