In my zelda twilight princess i am unable to access the items screen and the weapons screen.

you can use walkthroughs and cheats to help you with zelda twilight princess

Unfortunately zelda games in general don't support I game cheats. Occasionally you might find glitches in the game, but nothing like unlimited money or rupees (I wish) . You can however you can search how to complete side quests and collect all the bugs and so forth.

you dont have a mission to be exact but what you can do i go to the farm and learn how to ride Epona

Type Zelda Twilight Princess Walkthrough into any internet search engine. Something should come up read through required section

You need to defeat the Baboon boss in the Forest temple. If you need help getting him go to this walkthrough:

http://www.gamefaqs.com/console/wii/file/928519/45837

On Youtube there are many videos of how to fix a game. I'm trying one right now.

ign.com

The disc might be scrached, you can take a soft silky dry cloth and try to clean it, if it doesn't work you can try and get a new one.

You need your disc cleaned - take it to a local Play N Trade store and they should be able to get it back to work correctly

If you mean the gate with the Twilight Bulbins on the other side turn on your senses and dig.