Sound suspiciously like a virus attack! If so Trainables solution is, unfortunately, probably the best solution. (Reinstall)
But, you could try this.
First, open up a Global Admin account.
Open a command prompt (Run as Administrator.)
Type the following command and enter.
net user administrator /active
Log out and see if you have a new alternative login, as well as your existing one. If not, do it the long way.
Shut down the computer for a cold boot. Tap the "F8" key as you are booting.
Select "Safe Mode with networking" from the boot menu.
Log into windows 7 with your personal account that holds the administrator access.
Open a command window (START--->RUN--->CMD.exe). At the command prompt type the following net user administrator /active
Log out and log back in as administrator.
Another way
Go to Start
Type Control UserPasswords2. (or Open the Start menu, and type lusrmgr.msc )
Click Advanced.
Click Advanced again.
Select Users.
Select Administrator and untick the the box “Administrator is disabled”
Now log out and login as Administrator.
The action leaves you a little more vulnerable to outside attack. Not a big issue if you are confident with your anti virus control etc.
Hopefully the first will work!
You should find you can now edit the Registry. I don't know which solution you have tried, but this is one from Microsoft:
Please backup the registry, or the OS, first.
1. Go to "Start", "Run", and enter "regedit"
2. Maximize the "HKEY_LOCAL_MACHINE" window.
3. Scroll down to "SYSTEM\CurrentControlSet\Enum"
4. With "Enum" selected click the "Security", "Permissions" menu.
Note: At this point you will probably notice there are no permissions on this key.
5. Click "Add".
6. Add the group "Everyone" and the user "SYSTEM".
7. Select "Everyone" and check "Read" ONLY!
8. Select "SYSTEM" and check "Full Control".
9. Click the "Advanced" button at the bottom of the window.
10. On the Advanced window check "Reset permissions on all child objects..."
11. Click "OK"
12. On the warning window click "Yes"
13. Close the registry.
I reccomend, assuming this has worked, that you disable the "Admin" user again.