My sandisk 2gb pendrive gets detected but does not show memory

Firstly, it may be because of a virus infection. But you can try opening pen drive by typing its path( i.e. letter) in the explorer address bar and see if you can go there. If you can not, try formatting it and you should also check errors on it by right clicking on it> propeerties> tools> check now. Mostly a virus infection is the prime cause, so either format it (not with quick one) or scan it with good some anti virus.