Dell Inspiron 1545 — Poor Service, Defective item

I have purchased a new dell inspiron 1545 laptop in october last week.
Configuration is as follow:-
3Gb Ram
320Gb Hdd
Intel Cor2Duo Processor 2.2 Ghz

Problem:-
I m not getting sound from my laptop speaker, not even from my headphone. I asked the distributor then he told that dell doesn't offer software warranty.
As i didn't get any drivers CD, i m unable to configure my laptop. Online dell driver download link also doesn't work most of the time.
I m suffering from this problem since i bought this laptop.

Another problem is:-

Whenever i attach laptop charger with this laptop, my screen automatically dims, and when i remove charger it automatically start brightening.
i have seen lot of laptops in which whenever we connects power cable it automatically starts brightening which is totally vice versa with my condition.

i think i got defective piece, i want dell persons to replace my laptop or repair this problem along with my sound problem.
Sound problem is very critical problem as i generally need sound for various kind of presentations.

it want them to do it as soon as possible.