Hi and welcome to the WTT forums.
Sorry to hear of the problems with your machine.
It is possible to run some applications from an external USB drive but it is not always straightforward,
Most applications will try to install to your C drive and you will need to be pretty quick on your feet and also quite lucky to get them all to run if installed on an external drive
More information is available on this from here:
http://ask-leo.com/c...rnal_drive.html
If you think that the machine in question is infected then you should follow the directions here:
http://forums.whatth...ers_t34502.html (How to download HJT and where to post it)
Once you have followed the directions and posted your HJT log in the appropriate forum (not here please, as we don't analyse logs here in this sub-forum) it's important that you wait until you receive a response before making any further posts in that thread as the malware fighters look first for topics with zero responses.
Regards
paws