BleepingComputer.com: No HDD boot after new power supply

My computer started blinking out a few times, and then quit and would not turn on. I decided it was the power supply, went to Best Buy and bought an off-the-shelf power supply and installed it. My computer is a Dell XPS 400 and originally had a 375W power supply, and I replaced it with a Dynex 400W power supply. I was able to get it to boot up to Windows (7) just once, although not on the first boot. Currently when I start the computer, I get past the splash screen, and then reach a black screen with the blinking underscore in the upper left corner of the screen. At one point, while the computer was sitting on, I heard a series of clicks, but it had no effect on the blank screen. Could a difference of 25W make a difference? I would think slightly more wattage wouldn't be a bad thing, but wonder now. Does anybody have any ideas? Your help is most appreciated!

Thank you,
Tom

Run a diagnostic test for the hard drive.

Not all power supplies are created equal. Cheap power supplies deliver erratic voltage ranges that some hardware cannot handle. I have a brand new Retail Plus bought at Staples that will not run anything. I returned it and they gave my another that sits in the box it came in gathering dust because it will not run anything either.

The wattage is fine, only less wattage than what you require will cause problems.