If you are manually setting the wireless connection and geting a connection then the settings must be correct  or else it would'nt let you connect. Make sure you are right next to the wireless router or access point because a few things can interfere with the wireless signal like microwave ovens, metal objects or magnetic fields. Also check the signal strength to see if it is weak where your system sits. You haven't mentioned what sort of wireless card you are using or if it is USB etc. There are very few details in regards to the network being used so more details would be required.