If I had to just guess from the discribed simptoms I'd say it's the kernal or hang-time during normal boot of loading the SD card.
The state you're discribing is known as a "soft brick" and "boot loop" among seasoned Android SuperUsers; try the quoted terms along with your device's name in a google search to find other users of your device model that have solved or worked around these issues. There are many forums dedicated to helping with spicific devices but I always go back to XDA-developers and thier forum's members to truble shoot my rooted Android devices. For many devices there's an online resource for flashing ROMs, Kernals and others that goes by the name of C.A.S.U.A.L. a perpious built scripting tool written by a developer I've watched for many years (in a totaly non creepy way) for hacking nearly every device I've owned. The author also provides tools such as jOden which easiy flashes Samsung devices with your PC's browser.
Additinal hint on searching with Google
The above can be added to the end of your search quaries to nerrow down the results considerably.
Here's one link I pulled from using the above tricks mixed with your device's specs;
http://forum.xda-developers.com/galaxy-nexus/development/gnex-toolkit-v11-1-0-drivers-backup-t1392310
You've stated that you can get back into CWM, this means you're not the owner of a "brick", so long as your device can be booted into either "Download Mode" or the "Recovery" screens you're device can be salvaged.
To re-flash your device with a PC you'll need to be in "Download Mode" and flash with a PC via USB, however, before trying these options you should first attempt to re-boot into "Custom Recovery" and restore from a known working backup. Often these bootloops can happen after messing with a "build.prop" setting or if you have moved an app over to SD that wasn't designed for it. The SD card takes a bit of time to load so if you've soft-linked a system asset from it, the asset could be loading during CWM booting process (ie loading the SD card to look for backups) and thus able to be loaded during the rest of the boot but otherwise called before loading the SD card.
** Download Mode is a differant button combo than CWM **
Best bet to keep from losing anything is make a backup now! or the next time you can boot into CWM. Even your non-working setup is usefull if you need to recover a text message or debug the differaces between working and non-working setups. Also it is really easy to do something dumb {I've been close} when frustrated, so give a gift to your future self, on the off chance that it is needed.
Then backup your SD card compleatly to another drive. Then;
reboot into CWM
These are the steps I follow for the many Android devices I work with and similar steps are preformed for the even older devices. Ocasionally I will have to flash back to stock and re-root a device but this is rare; more often than not it is a bad kernal or bad download of a ROM that does this to my devices.
Oh and bootloops that don't let you get back into CWM without a cold start or PC flash is usually from TWRP to CWM backup/restor or flashing from one over the other in properly; similarly this sometimes happen when moving from stock to Super User; look up BML vs MTD for more info on that. But this is why most root methods have what is usually called "clean"-keral to flash just before going to CM or why when using Oden you have to un-check 'auto reboot' for certain operations. The stock recovery will attmept to overwrite your newer recovery.
Oh and before I forget here is the link to C.A.S.U.A.L. Google code page
https://android-casual.googlecode.com/
The author has also made some really fantastic YouTube terdown & repair videos and has posted some really interesting articals.
