Screen blackout every 3-4 minutes

I just upgraded my Gateway DX4300-03 computer from Windows Vista 64-bit to Windows 7 Home Premium, and ever since, my monitor has been periodically switching off for 1-2 seconds as if it lost the connection, then refreshes. When the screen comes back, the mouse is centered on the screen. This issue did not happen with Vista.

I have tried updating my video drivers(to ATI's version 10.1), and installed all the windows updates, and still the same issue. I've also uninstalled the ATI drivers to force windows drivers for the card, and I get the same thing (although the off time seems to be shorter). It seems to happen no matter what the computer is doing (playing a game, browsing folders, completely idle).

Any suggestions?

The system contains an AMD Phenom X4 9750 processor, an ATI Radeon HD 4650 video card, 8GB DDR, 1TB Hard Drive. Full specs are here: http://www.gateway.com/systems/product/529668282.php

Also to note, I know the power supply is pretty small (300W), but again, it didn't have an issue in Vista. I was thinking about upgrading it to a 500W or bigger, but I'm not sure if it will help yet.

Thanks in advance for any suggestions!

The monitor is a Dell 19" digital, though I use the VGA connection through a KVM so I can run my older computer at the same time I could check later tonight if the DVI interface gives the same issue. I did not load the drivers from the CD that came with it, though the computer recognizes the monitor model number. I had not disconnected the cables at all during the upgrade.

I brought the tower and KVM with to work and hooked them up there (also have a Dell monitor at work), and have the same issue. Using the windows driver makes the "blackouts" much shorter, but just as frequent.

I have tried the Catalyst Control Center full 10.1 install, and the driver-only install with the same results for both.

I also noticed in the device manager that 2 adapters are listed. I'm not sure what that is, but it shows "ATI Radeon HD 3200 Graphics (Microsoft Corporation WDDM 1.1)" and "ATI Radeon HD 4650 (Microsoft Corporation WDDM 1.1)".

Haven't tried bypassing the KVM yet (IOGEAR CGS632U), but I will definitely give it a shot. I'll repost once I've done it.

So I tried unplugging the monitor from the KVM, and going direct to the video card (wireless usb/keyboard still through KVM). This seems to have taken care of the issue. I still have the windows drivers for the graphics cards rather than the ATI drivers, but since the issue happened in both, it seems like removing the KVM from the monitor picture is the answer. I can still use the KVM to switch the keyboard/mouse, but I'll use the dual-input monitor for now to switch between machines for video.

I had tried updating from the device manager previously, but no difference.

Thanks to all for your help!