First check all of your dependencies including plugins and children in the dependency tree,
try to replace snapshot versions with release versions,
as snapshot versions will always look for a later update, whereas
release versions are deemed to be stable and updates are not expected for the same version number.
Secondly, assuming that you are working on a LAN, I would suggest that you install a local maven repository manager such as Nexus, and then redirect your artifact requests by setting
<mirrorOf>*</mirrorOf>
in your ${user.home}/.m2/settings.xml
This will enable your downloads to be resolved quickly against a local mirror, rather than continually checking against repositories on the internet.