My internet gets slow over time.?

I have a desktop computer that my cousin built for me. Works great and no problems. Other than one. When i leave the computer idle, say over night or while i go outside or watch a movie the internet will just stop working. The problem was worse, it wouldn't work atall, not its just painfully slow and dosnt load stuff. I asked my cousin and the problem was fixed. It was the network card, set to turn off after a while in order to stop bugs and bots to get in when im not uing it. It still does this. I would turn it off but it takes a few minutes to start back up, unlike my laptop. So id rather just be able to turn off the screen and speakers and get back to it a few hours later. Another thing is that when this happens, xboxlive will still work, my laptops internet is fine and everything. It not my internet its the computer. Any help please? I would also say that the problem got half fixed when i turned the network card on "always"