Bad Wifi network connection/signal

Hi, I'm using a brand new Optiplex 7010 desktop with windows 8.1, and I'm experiencing some problems with my domestic wifi, i'm no computer expert. The network adapters are:

- Intel(R) 82579LM Gigabit Network Connection

- Mini DW1530 Wireless -N WLAN

Problem: The wifi signal is very poor, very unstable and constantly disconnecting, I cannot use it for more than a minute or two without reconnecting. What is strange is that, side by side with my desktop there is an old notebook (which is the one I'm writing this message with) that connects plain normal and full speed with the same network connection (it's  network card is Atheros AR2427 Wireless Network Adapter and with Windows 7). I've tried shutting down the notebook and using only the desktop but the problem remains the same.

Please help! 

Thanks

Ps: Apologies for my bad English