I may have a unique issue, but I hope not because I can't resolve it 
My Nexus 7 is rooted, but just a root, no custom ROM ever installed, I only rooted to be able to connect a USB thumb drive.
When the 4.2 updates was pushed out and it got to my device it asked to reboot which it did but 4.2 did not install, I am still on 4.1.2, BUT ever since then my apps will not update, I can't install any new apps and I cannot get into Recovery Mode to sideload the 4.2 update using adb.
When I attempt to get into Recovery Mode, the tablet will just boot back to normal. Here are the steps I have taken to try to boot to recovery with no luck.
1. USB Tethering (enabled)
2. Power down
3. Hold down Power+Vol Up+ Vol Down (boots to Android with stomach open)
4. Plug in USB cable to Nexus 7 (cable is connected to PC first)
5. Use arrow keys to switch to Recovery Mode
6. Press Power button to boot into Recovery
Like I said above these steps, this just causes the Nexus 7 to boot into regular Android 4.1.2.
Has anyone run across this or know a way to fix my issues with apps updating or updating to 4.2? Thanks!

My Nexus 7 is rooted, but just a root, no custom ROM ever installed, I only rooted to be able to connect a USB thumb drive.
When the 4.2 updates was pushed out and it got to my device it asked to reboot which it did but 4.2 did not install, I am still on 4.1.2, BUT ever since then my apps will not update, I can't install any new apps and I cannot get into Recovery Mode to sideload the 4.2 update using adb.
When I attempt to get into Recovery Mode, the tablet will just boot back to normal. Here are the steps I have taken to try to boot to recovery with no luck.
1. USB Tethering (enabled)
2. Power down
3. Hold down Power+Vol Up+ Vol Down (boots to Android with stomach open)
4. Plug in USB cable to Nexus 7 (cable is connected to PC first)
5. Use arrow keys to switch to Recovery Mode
6. Press Power button to boot into Recovery
Like I said above these steps, this just causes the Nexus 7 to boot into regular Android 4.1.2.
Has anyone run across this or know a way to fix my issues with apps updating or updating to 4.2? Thanks!