What is the operating system, the firewall, and the antivirus installed?
Such issues are often caused by an incorrectly configured firewall, remnants of more than one AV on the system, and last (but by no means least) malware on the computer.
Had any virus alerts recently? Run any scans?
Try scanning with
MBAM (Free version available at that link - update it after installing and before scanning - a quick scan will suffice) and have it delete anything found. Post the details if any. (Like, the scan report.)