Lost internet connection to my 2nd wireless p.c

Question

iam running 3 pc's in my home at present. no1 pc is thru optus cable & other 2 on wireless setup thru linksys 2.4ghz broadband router,pc 2 working on wireless upstairs ok.i moved pc 3 from downstairs to another room upstairs and have lost our internet connection. now we are picking up a weak internet singal from our neighbours pc but signal strength is low & still no internet connection.do you have any suggestions to fix my problem.