Hi I too have been getting blue screen hang on my Lennovo T400 laptop. Googled around quite a bit and found too many solutions. One that worked for me is as below-

Note: The links given below are for models T400 and T400s in lennovo site. If your model is different, please click on drivers and software link in the same site and select your appropriate model number to get the latest driver files.

1. Update BIOS from Lenovo site

2. Update your power manager from Lenovo site

3. Uninstall your Graphics driver.

4. Install any driver cleaner software. Just google and you can get one. This is used to cleanup driver files left behind by the uninstaller. Believe me, there are files....

5. Remove your network cable and restart your computer in safe mode (F8 key during startup). If you don't remove the network cable, windows will try to connect to the internet and try to install a graphics driver automatically from internet. Once re-started, run the driver cleaner to remove all ATI graphics driver files.

6. Reinstall latest graphics driver available at lennovo site (Make sure you install the catalyst control center that comes along with it. This will be checked by default. Just don't choose to install the driver alone).

7. Make sure that the "Enable power play button is UNCKECKED in the Catalyst control center.

Restart and that's it. No blue screen there after  Smile Smile Smile