Linksys wireless adapter problems,.?

Okay... One of my computers which haves a antenna adapter thingy sometimes loses connection and sometimes it just does not connects at all the router... I have 2 more laptops and they both work with there there wireless cards perfect, so i know for sure is not any interference,... So i am wondering if its the antenna? Should i just go buy a new adapter for the PC? .. Oh and the problem is, when i do a repair most of the times it wont find the default gateway, and when i put it manually it does not connect.