It's valid to disable wireless security as an aid to installing or troubleshooting -- indeed it is often essential.
Have a look at the literature which came with your router and get into the router's setup screens. From there go to Wireless Security and untick the option for security (or deselect WEP or WPA).
While there also go to area entitled Access List or similar -- it's a facility to filter users in or out depending on their MAC ID (that's a unique number assigned to every wireless adapter etc.). Disable that permanently as it'd pretty useless and often causes problems.
Once you've finished troubleshooting it is, as Saga says, essential to run with WPA PSK TKIP security enabled. If your wireless adapter or router don't work together with security enabled, change one of them.
Unless (of course) the nearest neighbour or roadway is more than 100 metres distant.