Multiple issues w/ new card(artifacts, crashes, only works horizontal)

I snatched up a $70 HD 4890 on Black Friday from Newegg.

However... After installing the card, the computer only works when flipped horizontally (case is meant to be vertical). This doesn't really bother me, but it is interesting.
The real problem is that now the computer will only properly boot a third of the time. Usually, I get to the boot logo with two streaks of white down my screen and then the blue screen with a lot more artifacts (this happens 100% of the time when the computer is flipped vertically). When I do get it to boot, it will often give me the error "display driver stopped responding and successfully restored", followed by the screen's colors being messed up and often flashing between the correct colors and the "messed up" colors.' This makes it unusable and I have to reboot.

I have a Studio XPS 7100 from Dell (I know, I should have built my own, but I started with this and decided to upgrade later)
Here are the specs I do know:
460W PSU (I think I recall seeing the brand Delta Technologies)
HD 4890 1 GB
Phenom II X4 2.8 GHz
8GB RAM (I don't know the brand)
Seagate 7200 rpm 350gb + 1tb
Dell's proprietary motherboard

I know my PSU does not have enough power to run this properly. Whenever I do get a good startup, I can play games at high/ultra perfectly. What I was wondering was if I should upgrade my PSU to a 600w even though there seems to be possible problems with my connector or the actual card. I tried taking it out and putting in my old card (5450) and it worked same as before. I don't think the problem lies in the actual card, but I wanted to ask you guys for help.

Thanks.