Here is what I have had to do when a 7970 crashed.
http://www.cisco.com/en/US/products/hw/phones/ps379/products_administration_guide_chapter09186a00801d66cb.html#wp1087544
Factory Reset
A factory reset of the Cisco IP Phone restores the phone is reset to its factory state. This procedure reloads the default firmware image, deletes call histories from the call logs, and resets all configuration settings to their factory values.
To perform a factory reset of a phone, perform the following steps. The phone must be on a network that supports DHCP.
Procedure
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Step 1 Unplug the power cable from the phone and then plug it back in.
The phone begins its power up cycle.
Step 2 While the phone is powering up, and before the Speaker button flashes on and off, press #.
Each line button flashes on and off in sequence.
Step 3 Press 123456789*0#.
You can press a key twice in a row, but if you press the keys out of sequence, the factory reset will not take place.
After you press these keys, the phone will go through the factory reset process.
If this does not work you will have to RMA phone back to Cisco. Out of our 400 7970 phones I have only had to return 6 phones becasue the reset did not work.
Hope this helps.
