WSUS 3.0 - new install - won't push out updates to all PCs

[Sulolab]

We have installed WSUS 3.0 on a new server and all system are showing up in WSUS but most of them are having approved updates in "Need to install" status. Any ideas why it might be so??? We have pointed Group Policy form old 2.x server to our new 3.0 server because of which system are appearing in WSUS 3.0 but for some reason many updates have not been installed. Is there anyone who can help me out on this matter???

[hindustnidude]

If it has been some time since installing WSUS 3.0 then just let me know your group policy complete settings to have a better idea?? Sometimes new server has to download update content which takes some time. If that's not the case then you can download Client Diagnostics Tool on affected clients and post back the result you get for further help.
If there are any machine that are receiving the updates without any issues then you can try running rsop.msc on one of those PC'S and cross check WSUS settings. If you imply want to kick off the update process then you can type "wuauclt.exe /detectnow" without quotes in command prompt and hit enter.