XPS M1730 Slow computer / battery problems / cant play HD Video

I got an Dell XPS M1730, the specs on my computer is:

Intel® Core™ 2 Duo-prosessor T8300 (2,40 GHz, 800 MHz FSB, 3 MB L2-buffer

2048 MB 667 MHz Dual Channel DDR2 SDRAM

2x 256 MB NVIDIA® GeForce® Go 8700M GT

I have serval problems,  the laptop is only 1 year old and i have used it well and taken care of it.

The first problem is the computer seems very slow, mutch slower than it was when i got it.

Second problem:  When i play .mkw filer, like HD movies, and big movies it just comes alot of diffrent collors and scratcy sound. Like the computer is to slow, the strange thing about this is that it wasent like this before. I became so over the night..

Thrid problem: The battery doesent work, i cant turn it on with the battery in, it is all dead. Arent the battery supposed to work longer then a year? I havend used the battery mutch, the computer is normaly docked at home.

The things i tryed to fix those problem over:

I have taken a clean install of windows vista, formated the hardrive completly and installed drivers from xps support side. Still dosent worked, updated the graphic drivers, etc

Anyone have an idea what the problem can be?

Im happy for every tip you can give to get this problem solved, it was an expensive computer and want it to work properlay.