8800GTX and 450W psu

Probably not.
What is the +12V amperage on your PSU?
Even if it is high enough, it would be a good idea to upgrade to the 620W PSU.
The GTX is quite a power hog.

http://global.aopen.com/products_detail.aspx?Auno=2520

The psu webpage.

it's not just the 450 part, it has to have enough amps on the 12volt side and not just the 3.3 and 5 volt side. A lot of older power supplies had a lot of power on the 3 and 5 volt side and less on the 12 volt. Problem is now that new stuff use more power on the 12 volt side and les on the 3/5 volt side. Newer cards like the geforces pull it all off the 12 volt side. You might have 450 ( peak) but it might only be 350 or so continuous, plus it might be on the 3/5 volt rail which does you no good.

You need to post your model number and such. A good place to go would be jonnyguru.com, their main focus is power supplies and people over there know a lot about them and what is inside. You need to give us the model number and a picture of the sticker though to be able to tell for sure

Hmmm...it might work, but it could also die, depends on the quality of the build and if your gonna overclock, but I think it is pushing it on a GTX. I am no expert though, so I would go to that site and ask the people that actually test power supplies. A lot of inexpensive supplies fail WAAAY before their rating around 50% load on some, so it is best to see if anyone over there would know.

Agreed. It seems that this is the case with my psu as well.

Model Z450-08APA

+12V (1): 18A
+12V (2): 18A

+3.3V: 30A
+5V: 28A

The corsair620 has 24A on 3.3,and 30A on 5? Is that ok?

btw, im also a bit shaky on the dying part... i think it wud be pushing it to the limits with a gtx (esp when oc;'ing).

Ive used a 420 watt with 18 amps per rail, a bit better quality than yours, with a G80 GTS, but I felt I was coming close to maxxing it out. I wouldnt do it, not sure about aopen, and its no better than my old enermax