When I open the start menu and write in run "regedit" the message told me can not access
Ask your administrator ,no one use my PC what is wrong please help

Chances are your account is not an administrator account. Just beucase no one uses the computer doesn't mean that your account has not been setup as a "Limited" account. If you do not have administrator privledges, you will not be able to run regedit.

Do you have a true need for using regedit?

I need to acces my registery to control with my PC .
I am the administrator of my PC and my account has the administrator privledges
This problem appered recently, in past my registery was accesable

I HAVE HACKED YOUR COMPUTER!
Hye! Just joking!try the following:
Click start>run.type gpedit.msc and click OK.at left side you will see User Configuration.under it there will be administrative tempelates.double click it to open.then there will be system under it.click on it. At right side many settings will come.double click on the one which says that "Prevent access to registry editing tools".double click on it to open the settings dialog box. Choose the option "Not Configured" and click Apply and the click on OK. Now your problem should be solved.