I reloaded Windows 7 onto a laptop recently and it was stuck in checking for updates forever.
Heres what I did to sort it -
Go to control panel, system and security, windows update, change settings...and... in the drop down box, set it to never install updates. Restart computer. Ignore any warnings about windows update being turned off. Then first install
KB3020369
https://support.microsoft.com/kb/3020369
then install KB3172605:
https://support.microsoft.com/kb/3172605
Restart your computer, go back to control panel, system and security, windows update, and turn on windows updates (to whatever delivery option you prefer). Then click "check for updates".
After 15 mins checking for updates it found them all and started downloading.