Computer help forum: Monitor enters power save mode immediately after startup

Hi all. When I power on my desktop, my LG LCD monitor behaves normally for about 10 seconds until it turns black and says Power Saving Mode, with the monitor light changing from blue to orange. The computer seems to continue booting up normally, as I can hear the Windows startup music when Windows eventually starts.

When this first occurred, I did a hard reset to try again - this time my system displayed the menu that gives the option to reboot in Safe Mode, but before I had a chance to make any selection, I lost video again, after about 10 secs. Tried restarting a couple more times but always with the same results..... even if I try to enter the BIOS setup screen, my monitor will still lose video signal after just a few seconds.

I tried switching my monitor's DVI cable over to the second DVI output on the video card, and that solved the problem. The following day the same problem occurred on the second output, and since then both DVI outputs on the video card produce the same problem.

I've tried searching for possible solutions, and some other internet threads out there recommend pulling out and reseating the video card and memory, making sure to clean any dust, but that didn't seem to help my problem. I've also seen some threads mentioning that it may be a problem with the motherboard battery forcing a low power mode. But removing and replacing the battery doesn't solve this problem either.

I've also read that there may be some motherboard power saving settings that might interfere with the OS's settings, but unfortunately I can't review/edit these settings because even if I try to go into the BIOS setup, I still only have a couple seconds before the screen goes black.

Unfortunately I don't have another monitor or DVI cable to test this with. My card has an S video output but I don't have a cable. Since I'm clueless at the moment, I'd rather not spend money on new cables unless I'm fairly certain it would solve the problem, but if you guys have a good idea I would take your advice I do have a video card from an old desktop, but it doesn't fit into the same slot on the motherboard.

Here are my specs as well as I can remember them:
Monitor: LG LCD
Video Card: ATI Radeon 56XX or 57XX 512MB
CPU: Intel Quad-Core 3.0GHz
RAM: 8GB
OS: Windows Vista
My system is about 2.5 years old.

One other piece of info: A few months ago I used to experience some incidents of pixellation on the screen. This would occur once every few days over the course of a couple months, but then it stopped. Dunno if this is related but it kinda indicates to me that my best solution is to try replacing my video card.

Sorry for the long post, but anyone have any ideas? Thanks so much for any help you can provide.