Installed second vid card for dual monitors, now it hangs up upon startup. Power supply issue?

I recently installed a second video card in my HP dc5100 to support dual monitors. Now when i boot up the first time in the morning, it freezes when booting into windows (at the windows start up screen with the status bar). I hard shut off and then wait about 5 or 10 seconds, then turn it back on. I am thinking it might be a power supply issue, but am wondering if how i am doing it now is harmful to my computer.|||Sounds more like a driver conflict to me. Make sure you have the latest drivers for both the graphics cards. Seriously doubt power problems.|||i guess, its a driver conflict. try to reinstall driver for VGA(cideo card), or u can do one more thing, uninstall one video card, so u left, one videocard and one plugin for internal chipset, connect one monitor for video card and another monitor for chipset and then try.