Update your post to include full system hardware specs and be sure to include the wired network adapter: make and model.
First, verify that only one network adapter is enabled on your Desktop PC. Either wired or wireless - not both.
Second, download, reinstall, and reconfigure the wired network adapter's drivers. Do so via the manufacturer's website. Ensure that you download the applicable Windows 7 driver.
Third, the cable may be okay provided that there is a direct connection between Desktop PC and router. However, if there are other components such as switches, wall jacks, powerline adapters between Desktop PC and the router then any such component could be the cause of the disconnections.