Hello Serbitar, and welcome to Seven Forums.
What firewall program are you using? If it's not Windows Firewall, then temporarily disable or uninstall it to test if Windows Update runs properly afterwards.
If you are using Windows Firewall, then you might try OPTION TWO in the tutorial below to reset Windows Update to see if that may be able to help. Windows Update - Reset
If still no help, then you could do a system restore
using a restore point dated before you had this issue.
Hope this helps,