By not coming back on...do you mean it wont even power up? Have you tried perhaps removing "all" power from the system...including the battery. Then reset the system bios to default if the Thinkpad allows for that process. If there are not specific instruction on reset/clear cmos then crack it open and remove the reserve battery then reinstall it an see if that does anything. Just and idea, perhaps you have already exahusted these ideas. good luck.
I was just on the IBM site..have you tried these proceedures?
Load the original configuration in the BIOS.
* For ThinkPad A, R, T, and X series systems
1. Turn on the computer.
2. While the "Press F1 for BIOS Setup Utility or the blue Access IBM button" message is displayed at the lower left area of the screen, press the F1 key. The BIOS Setup Utility menu will be displayed. If a password prompt appears, type the correct password.
3. Press the F9 key and then select Yes to load the default configuration.
4. Press the F10 key and then select Yes to save the configuration changes and exit.
* For ThinkPad 600, 600E, 770, 770E/ED, 770X, and 770Z systems
1. Press and hold the F1 key, then turn on the computer. Hold the F1 key until the Easy-Setup menu appears. If a password prompt appears, type the correct password.
2. Select Config.
3. Select Initialize and then click OK.
4. Click Exit, click Restart, and then click OK to restart the system.