inspiron 8200/wireless issues

I just reloaded my laptop with windows xp because of major problems, now it seems i cannot get on the internet,it recognizers my wireless modem but refuses to connect. any ideas??

My other problem is when you open up my screen picture is 4"x 6", any ideas how to enlarge the screen to its full size??

I"m not very good on computers and need all the help i can get.