First of all, download WinPatrol. Install it and then run it. Now, click on the Startup Programs tab, and look for the following programs -- if found, click on them once, and then choose Disable. This list are the programs that I either don't know / think that they could be the cause. It's up to you whether you wish to disable them or not -- this does not remove them, it simply makes them not startup...
8e6Home Internet Protection Services v.4.5
Click to Meet Conference Client
Intel® PRO Network Connections Drivers
Quicken Basic 2000
Rocket 2005 DEMO VERSION (1024x768) Screen Saver
Rocket DEMO VERSION (1024x768) Screen Saver
SpaceCAD 3.1 (Build 284)
TurboTax Basic 2004
VNC Free Edition 4.1.1
WeatherBug Browser Bar - powered by MyWebSearch
Once done, restart your computer and then try to share files -- can you?