I have a T400 that I had to reset to factory settings (2008) . After resetting I began to download and install all the Windows updates. For one set of updates, after restarting the computer my T400 began taking 10 minutes to boot. It continues to do this even one week later after all the updates have been installed. The screen goes black for 10 minutes and then I get the ThinkPad screen and Windows boots without a problem. The delay takes place before the BIOS screen appears.
What could be the problem?
One of the updates could have been a BIOs update, which needs to be initialized.
Try initializing the BIOS update.
Go into the BIOS, press F9 - load default, F10 - Yes
Also try removing the BIOS battery for several minutes.