Dead slow when extracting rars, or copying files.

Hey guys, I'll sum my problem shortly:
-extracting RAR files using Winrar or 7 ZIP is very very, about 1:30 hour for 2.5 GB.
-copying files from other computer to mine is very slow as well: starts with speed of 12MB\s and falls pretty fast to 0.5MB\s.
- I believe I should mention- on wednesday night my computer was slow as a turtle, and it took him 5 minutes to open control panel. installed a new windows update, and it works just fine now. and then I discovered that rar's problem.
the steps I did so far:
-reinstalled winrar and 7zip.
- clean boot, check disk, windows memry check, some tool of my MS which said everything is fine with my computer.
- AntiVirus scan, malware and spyware scan, CC Cleaner.
- in Device Manager, my IDE stays in DMA mod, it doesn't converts itself to PIO mod. however I reinstalled my IDEs.

what I'm doing now: trying to defragment my disks. however I dont believe it'll help. windows says: (1% fragmented) so its not such a big problem I believe.

I used google,and seen about 7 or 8 threads around the internet of people with the same problem as mine, or with similiar one. however, I couldn't find the answer there- since no one gave her.

details on my computer:
Windows 7 32 bits, 3 GB RAM, Core2Duo 2.13GHz.

p.s- I tried to extract the same files on another computer- a laptop core2duo 2.6GHz and 4 GB RAM, and it went smoothly, and finished in 3 minutes.

I would really appriciate any help. thanks in advance.