Is there malware specific to Dropbox that blocks access and acts as a trojan?

A friend uses Dropbox to store and retrieve photos required to complete inspection reports. He is in the field daily and not near the office for months at a time. Recently, his dropbox account became inaccessible to him from either laptop. Then the main laptop started responding more slowly than usual and eventually even his browser was not as cooperative. He contacted a place to fix it, however since he is on the road they must attempt to do the work remotely.