I have two computers hard-wired into the router and a couple of laptops and tablets connected via WLAN. The WLAN works perfectly fine until my computer is turned on. The other hard-wired computer dosn't affect it at all. When my computer is turned on the WLAN signal disappeared completely for the laptops and tablets like the router has been switched off (my computer doesn't have any form of WLAN card in it only RJ-45). When turned my computer off the signal returns.
I have run a full virus scan on my computer and it has come back clean, I've tried disabling my firewall to see if it makes a difference but not change. My system is Windows 7.