Brand new Radeon 9800 Pro problem, please help!

I recently purchased an ATI Radeon 9800 Pro with 256 and a 256 bus from Newegg, I'm not a hardcore PC gamer or anything, so the 9800 Pro offered enough to make World of Warcraft run better, which is basically why I bought it. Now, I had upgraded from an awful 9600 SE (which I received as an XMas gift 2 years ago and didn't realize till just recently that it only had a 64-bit bus), that gave me crappy FPS and no frills, but was very, very stable. I've played WoW for like almost 6 months now with no problems, added RAM about a month ago, no problem there, still very stable, the game literally never crashed one time during this card's life. Now, when I got the new card, I threw it in, and basically that's when the nightmare began. I installed the drivers on the CD and I can't exactly remember how well those worked right off, I don't even think I attempted to play the game with those drivers, I just got Catalyst 5.9 from ATI's site. Upon doing so, my computer continually crashed like crazy. It would get into Windows, and oddly enough when I started any application that would use the internet, the computer would freeze or reset, or the monitor would display jumbled graphics like someone threw up a box of crayons on the screen.
I messed around with this for about 2 more days, removing devices from the comp like an ATI tv card I don't use anymore, a Sony DVD burner I don't use anymore, etc.... I tried juggling the power cords around, etc. No dice for about 2 days, it got to the point where the system stopped recognizing the fact that the card was there. I finally got it to work for maybe 20 mins at a time in Warcraft, and then it would freeze after a non-uniform amount of time. I would be playing and sometimes the game would lock a bit and the cursor would still move and then the system would hardlock, other times it'd freeze and go into a sound loop, another time the monitor shut off and came up with the "monitor is working" message like when the pc is off but the monitor is on except it displayed "out of scan range", another time the monitor went black and the light, amber, and went into a sound loop, it would freeze a different way alternating between like 4 or 5 different ways. After reading different forums and trying things ranging from "turning vsync off" to "turning off fastwrite" to "turn up the voltage to the card to 1.6 or 1.7 in the bios" and playing with the refresh rate (my montior is a Dell P1110 btw, if that helps) in both the game and on the desktop, I thought I finally got the problem licked ---- or so I thought.
For the past 2-3 days the card started working with almost current drivers when I took everything apart on my comp, reseated everything and decided to throw the card on it's own power channel. Windows now works absolutely fine no matter what I'm doing, and Warcraft seemed to work, unfortunately I was playing tonight for about 45 min and it went into a sound loop, the monitor shut off to the pc off "monitor is working" screen and then shut down to the amber light (i.e. - shut off completely).
I'm at a loss for this. This game and more importantly, my system worked absolutely harmoniously for a long time and then now that I added this card, somehow it was basically messing up my whole system. It feels like I'm missing something obvious here, like all of these problems have something in common, but I'm asking for the expertise of this board because you all seem to know very much so what you're talking about =). Now, as I said before, the old card (and I'm sure you all know this) had no extra power requirement and this has a power cord to it, and my power supply is an Antec 300w, could it be that I don't have enough power? The owner's manual says that this card requires at least a 300w PSU to run effectively, but I don't want to spend like $80 on a power supply if that's not going to be the problem. I'm pulling my hair out over this, seeing as I spent $200 to play one game, lol. So anyone's wise help would be greatly appreciated, also sorry for the book, I just wanted to make sure I didn't leave anything out, often times I know with computers the problem's usually in the details.... I posted twice to the WoW forums with no real response so far, so....
Thanks,
Brad

Is the heatsink loose on the card by any chance? Cause, when I had that card, my heatsink became too loose, and I started getting errors like yours.