Plz Help, If You Dare!

Okay thank you for reading.

Now i have a load of problems with my "rig" atm, iv built it on a small budget and if cant fix it i will probably have to replace it, but the problems im having, i belive shouldnt be happaning.

Now im about to list them:

• Internet Explorer, Keeps "not responding" every time i really dont want it to... as in alot of the time...
• Games all ways crash; They: Stop responding, Crash (quit out completly), Blue screen, Just plaing turn the system off (rare)
• I cannot install some programs. These are the main once: Itunes (I try and it says itunes needs quicktime, i have unistalled and reintalled, nothing helps. Next, graphics card drivers will not install they just quit the installer before it gets to the first page.

Now there the main problems that im havving but i get many other small problems that may help but i cant think of now just small things like computer lagg and things.

Now the problem is that this computer should be perfectly stable and have no problems the games im trying to run should easy be able to be run, but they crash alot.

Now things i thought/ think it mite be:
1) RAM i have taken both new sticks out and old sticks out sepratly to see if it was ram and it does the same thing with any config of ram.
2) The OS that im running, i think this as i seem to have problems mainly with the software side of things and when i tryed installing windows 7 for the first time i had many problems ike it not extracting fomt he CD propaly and then just not installing propaly. then inside the OS i cant install some drivers for things or some programs - Itunes
3) CPU? gotta be something...
4) Graphics card? maby

PC Spec:
Phenom x2 550 black AMD
Gigabyte M720-US3
6Gb Crosair RAM
Radion 5770HD
Windows 7 x64


Any help would be great
Thank you
Releah

I have tried multiple restores and gone to the extream of wiping my computer. Problem persisted as I reinstalled the OS the first time because I couldn't update my graphic drivers, and i was trying to update them to stop the crashing in games, but when I reisntalled the OS the problem got worse :s, I'm not bad with Computers but I'm stumped :s

Oo and thank you for the quick replay it's very welcome :)
Releah

Power supply is on the edge of requirements...might be starting to fail....especially if the 475 watts is the peak output

Would the power supply cause problems in installing software? i would have thought power supply would be fine as the power doesnt seem to fail just problems with things :S

A bad/weak power supply can drive you nuts....and bankrupt