Check for any malware blocking or using certain ports/connections.
use http://malwarebyte.com and run a scan to check for any viruses.
also check msconfig (start > run > msconfig) and go to the startup tab.
check if there is anything uncommon there.
try to look for the path and the license (company name) or name of the file.
try to put off your firewall and antivirus.
http://support.microsoft.com/kb/283673
for your antivirus it depends on the one you are using, I preffer using NONE and check with malwarebyte now and then.
