Brand new compuer runs slow

I built a new system using a asus p5nd 750i sli motherboard, a gts 250, 250 gb hd, 600w psu, 2 gigs kingston ram and an intel pentium d dual core processor 2.66 ghz.

After building this system and a fresh install of windows 7 32bit on the first run generally everything ran slow. Even going online on IE and firefox was slow to the point where i had to wait more than 10 secs for my email to load. Also when streaming videos the download was good but the playback was terrible. Every second it sticks so there is never smothe playtime always sticking.

Also i installed call of duty 4(not the least bit demanding) and i cant even run this on the lowest possible graphic settings without it sticking just like when i try to watch videos.

I took its temperature with software that came with the asus board and it says the the cpu and the motherboard are both 50 degrees Celsius.

What is the problem here? is it the heat that is dramatically lowering this pc's performance or is it something else. How do i fix it?