"Can I use a different watt power adapter?"に関する回答Yes, both power adapters should work fine for the Thinkpad. However, there may be limitations for the 65W power adapter: the battery will take longer to recharge and it might not be powerful enough for certain types of usage (ex. watching a DVD while at the same time running HDD intensive applications).
"How do I make sure my clock will continue to run?"に関する回答Because your laptop is old, replacing the back-up battery will insure that your clock will continue to function. See the link to our replacement guide to help you replace the back-up battery.
"How can I fix my flickering screen problem?"に関する回答This is a known problem among Thinkpad T400s users, and has been commonly linked to a faulty connection somewhere along the LCD cable (connections/cable itself): (1) At the terminal in the display itself (2) Along the cable which is a result of it being “pinched” or crimped (3) At the terminal on the motherboard If you notice the flickering resolving itself after flexing the screen (lightly) or that the problem only occurs in certain orientations then you are likely experiencing a wiring issue. If the screen only flickers at the start screen then it is possible that your drivers are out of date and you will want to update those before continuing. If you are convinced it is a hardware issue then you can remove the LCD bezel (the plastic rim that surrounds the screen) and check the terminal connection at the display. If that doesn’t resolve the issue you will likely need to go further into the guts of your laptop and check the connections at the motherboard terminal and along the cable. If you notice that...