Hi thanks for your help!!
i already did it and it works.
Im gonna write how i did it for other with the same problem:
The next steps are for enable recovery options in fastboot menu, so that you can install zip files and other options
1. First download Google Nexus_7_ToolKit_v4.0.0 and install it
It comes in this threat
http://xdaforums.com/showthread.php?t=1809195
3. After that enable USB debugging on nexus 7, to do that, go to "Settings > About tablet" and click several times in "Build number" it shoud say you are developer or something like that. Then go back to settings and in Developer options check the USB debugging mode.
4. Then start Google Nexus 7 ToolKit on your pc, by default its installed in c:/Google Nexus 7 ToolKit/ToolKit.exe
5. You can choose to update or not, but you can automatically update only if you donate.
6. After that you have to choose the version of you nexus by introducing the number and then enter, in my case y use option (6. Android 4.2.1 build JOP40D) for 3g version (i dont know if it works in only wifi so do it under your own risk)
7. Stop in the next screen and turn off your nexus, then turn it on in Fastboot mode, to do that i use (volume- and power button) first press volume down and holding press power on button and hold both buttons till a screen appers, and leave the nexus like this, and connect it to your pc via usb cable (be sure to have installed drivers when installing Nexus 7 Toolkit so that your pc recognices the nexus 7).
8. Then back to the computer i choose option (8 1-click for all unlock, root, reneame, custon recovery, etc )
9. Then select option 2 SuperSu by chainFire, cause when i did this i have android 4.2.1 on my nexus, the other option doesnt work for my version of android
10. Then I choose option (1. Clockworkmod touch recovey) and after that it will ask you to confirm so write yes and then hit enter.
11. Then wait till the process finish, and if everything go well you should see in your nexus aplications one called “SuperSU”
Then to enable tethering and hotspot
1. Download the enabletether-JOP40D that stridger (The creator of the post(Thanks!!)) upload or the enabletether-JOP40C according to your nexus 7
2. And connect your nexus 7 to your computer and save the “enabletether-JOP40D.zip” on the root directory of sdcard
3. Then turn off your nexus 7 and turn it on in fastboot mode again pressing and holding volume down and power up.
4. Then navigate through menu with volume up and volume down, to “Recovery Mode” and press power button to choose, then wait a little, it should show you a menu.
5. Here choose “Install zip from sdcard” > Choose zip from sdcard > 0/ > enabletether-JOP40D.zip or wherever you save it and press power buttom to choose it, wait to the installation ends, and that’s all, reboot your nexus 7, and look for the option in Settings > More Settings > Tethering and portable hotspot
Hope this help people like me that have this problem.
Thanks everyone