My macbook pro 2011 does not boot up.

Try reseting the PRam ( restart, on startup Hold down option, command, the leter P and the leter R. keep holding them down until you hear the start up chime for the 3rd time then you can let go)

I Like your thinking to do a backup whilst you still can, whilst its not completely necessarry as All your data is stored on The Hard drive which should be fine even if your machine was to never boot again it is definetly better to be safe then sorry. While the machine still works with another keyboard and mouse it dosent necessaraly rule out your Logic board, though my first impression is (considering both the keyboard and trackpad are not working) it sounds more like it could be just a minor power issue in which case reseting the PRAM and SMC (Shut down simultaneously press the control, option, shift and power button (willing it is a unibody macbook pro). You should notice the light on the magsafe change colour.) Should fix the issue.

Is the macbook pro a unibody or can you see tha battery on the bottom? if you can see the battery take the battery out and see if it is swollen at all and try booting with the battery not connected (just the power adapter)

To try and determine whether or not it is software or hardware, you could:

1. Run Software update, install any updates ( I noticed your profile says you are running 10.7.2, OS is currently up to 10.7.4)

2. Restart into Safe Boot- Hold down Shift Key upon start up until apple logo appears with a progress line. Does problem persist?

3- Create a new user - System Preferences/Users &Groups/ click the + (you may need to unlock the padlock).

- Log out of your user and log into the new user. Does Problem still persist?

4.Boot into recovery Partition - Restart mac, upon startup Hold down Command + R Until the apple logo appears.

Does problem persist in Recovery.

If The Keyboard and trackpad Work in any of the above, Boot into Recovery Partition and reinstall OS.

If the machine is under warranty ( you can check here ) I would definetly not open the machine as you could end up voiding the Warranty.

Has the machine come in any contact with liquid by any chance?

If you have followed all the steps i have mentioned Then I agree that it is starting to sound like it is Hardware related, In which case i Think it might be worth while taking a visit to an AASP (Apple Authorised Service Provider), though it wont hurt to reset the PRAM again and reinstall the OS.

If It is out of warranty and you realy want to open it up yourself then the Keyboard flex is the wide flex to the left (if your looking at it) of the RAM, there is a Fine locking leaver on the oposite side of the connector to where the flex enters, that you will need to flip up. you could try giving the flex a light clean (maybe just use a pensil eraser). Once again I would strongly suggest you take the Machine to an AASP though as its likely you dont have the apropriate enviroment to open the machine without the risk of causing more damage .

Just out of curiosity when you reset SMC, PRAM, Boot into SafeBoot & Recovery, Were you able to use the built in keyboard to input the commands (eg P, R, Option, Command) or did you have to use the external?

mmm maybe a Firmware issue?

Also try

Check System preferences/accessability -Keyboard- make sure sticky keys is not checked & Mouse & Trackpad - make sure "ignore built in trackpad when mouse or wireless trackpad is present" is not checked.

Unfortunatly I Wont have any computer/internet access untill monday so If that doesnt work it might be worth while Taking to an AASP.