I am stumped. I have a Belkin wireless router, and I'm using a D-Link wireless NIC. I am getting a very slow wireless network connection through my PC only. I did a speed test on my DSL connection, and it came out at 2.5 Mbps download speed. No problem there.
The problem is my wireless network. Even when I just try to go to my wireless router configurations it runs very slow. I thought the problem was my router, because when I connect to it directly with a wired connection it works fast. I brought a laptop home though, and connected it, and the internet, and wireless network was great. I also have a wireless PS3 on this network that works great too.
The next step was to test my NIC. I tried another wireless NIC, and am having the same problem. I am not having any trouble with pop ups or viruses, although I am going to try some deeper scans of these next.
This post is old but this answer could be useful for others.
1-Check if you have the NIC last driver version on your PC.
2-Check what kind of protocol the wifi router use and check if compatible with your NiC card, wifi b,g or n.
3-Change the wifi channel may be there are many wifi networks near to you.
4-Check NIc software for transmission rates limits.
Troubleshooting slow wireless connection 
Linear Mode
