Here's a hard one for you.

I just moved in a new house with a Wireless-G Router D-Link.

I got two computers: a 7 years old macbook ( OS 10.6.8 with a Airport Extreme Ox168C, 0x86 airport card ) and a custom built ( not by me ) Asus Desktop ( Windows 7 Family Premium with a D-Link DWA-566 Wireless N-300 Dual-Band card )

My macbook is using that network perfectly fine ( youtube at 720p without interruptions ) but my desktop is struggling.

At best, he will give me a low signal and the wifi will frequently drop ( and display an orange star )

I ran wifi speed tests with the two computers sitting exactly at the same place in the house.

Macbook: 1905kbps
Desktop: 566kbps

What I tried:
- Trying a new router ( D-LinkDWA-566 Wireless N-300 Dual Band )
- Running a scan with Avast and Malwarebytes
- Updating card's pilote
- Installing card via the Device Manager and reinstalling with a computer reboot
- System Restore