I just the had same problem. I figured out that Intellisense stopped working after I took some databases offline and doing an Intellisense refresh (Ctrl-Shift-R). I brought the offline databases back online, did a refresh (Ctl-Shft-R) again and VOILA! Intellisense is working again.
What a crappy design. Maybe the population of Intellisense's lists chokes when a database exists but is offline. Thanks Microsoft.