Oh! I read down and found that there is RESET Button on the back... its really small.
Slide off the Slip Off Back Cover (what's it for anyway?) and about a third of the way down the back off to the left side, you will see the RESET Button... you will have to poke it in with a small pointer or pen tip. when I originally had this problem, the RESET Button was so small that I did not notice it, and 'fixed' the problem by disconnecting the Battery, as I describe below, but apparently you do not have to go through that much trouble. Oh! I THINK my Calculator froze up when I disconnected the USB cable from the Power Adapter without first turning the Calculator OFF, so I would recommend not connecting or disconnecting the USB from Power unless the Calculator is turned OFF.
I looked in the Little User's Manual, and the RESET Button on the back is not mentioned. apparently the Manual was printed out before the Engineering Team noticed the FREEZE UP problem and added a RESET Button to fix it, and I suppose the Bean Counters that make the decisions at TI figured it would cost too much to edit and reprint the User's Manuals.
Original Post: Actually I came here to ask the same question. But what I DID DO, was to slip the removeable black back cover off of it, and that reveals the battery compartment held on by two small phillips head screws, which I removed, allowing the battery compartment cover to be removed. The battery is connected to the Calculator through a ribbon cable and what looks like a 5 or 6 pin connector. I pulled on the connector and I was able to remove it. This simulated a dead battery condition, and the calulator automatically shuts down. I carefully replugged in the connector; restored the battery ribbon connector to its guide slot, replaced the battery compartment lid; slipped back on the back cover, and turned the Calculator back on. It said that RAM Memory was lost, but then I CLEARED that message and added 2 + 2. It was working again.
I think what I did to freeze it up was to disconnect Charging Power through the USB Cable while the Calculator was ON. I guess you should turn the Calculator OFF before connecting or disconnecting from power.