Urgent: Still Not Able to Connect to the Internet

I have a Dell Inspiron 15R N5110, using a TrendNet Wireless Adapter, and using SkyWeb Internet Service. My laptop is a little over a year old.

On April 30, 2012, I had to have my hard drive and motherboard replaced by Dell due to some issues. It was replaced, but directly afterwards, I couldn't connect to my wireless internet when I was more than five feet away. I have contacted Dell several times about this and each time they give me the same answer: Reset/Uninstall the current connection, reconnect to the connection, and allow it to connect. Each time, it wouldn't work. Finally, after calling for the seventh or eighth time, I was told that perhaps my wireless card was bad (which I had suggested before, but the Dell employees told me that wasn't possible). So a Dell Dispatcher was sent to my house, my dispatch number being and my technician was Will. He replaced my WiFi card, ran an EPSA diagnostics test, to which all tests passed, and still couldn't get my Internet to connect. We were less than twenty feet away. He tried to suggest that perhaps it was because the wall was decreasing the signal, but that is not possible since my sister (who owns a Dell laptop herself) can connect just fine from anywhere in our home. He called Dell himself, who was told that I (the customer) should contact tech support. I contacted Dell support and was told to contact the wireless division, who has told me to the same thing as stated above (reset, re-install, connect). Since then, I posted on the forums here and received some help. I was  told to turn off the power saving feature under my wireless networks in device manager. That seemed to do the trick for a few hours. Then, it went back to cutting in and out. I can't go more than five feet from my wifi adapter anymore when I used to be able to go outside with it. My sister (as mentioned before) tested this a few days ago.

I have installed numerous drivers, and I'm not even sure whether I need them or if they're even working. I'm getting frustrated that for two months now, I have had this problem and no one seems to be helping me. I have classes for college coming up soon and I need to be able to connect to the Internet. I'm in desperate need of help and any will be helpful. Thank you.