I bought a 4gb 670gtx sc a couple of months ago so it's been running 306.23. I haven't opened the Nvidia control panel or anything for the last couple of months. I get another card today to SLI so I put it in and get the "Your system is SLI capable click here" message but it does nothing when I click on it. I see the Nvidia control panel in the system tray but clicking does nothing. 
 
Any time I try to install or uninstall drivers I get a 'failed' message. I've tried the stop/start services thing and even the minesweeper thing, but nothing works.
 
Any ideas?

Do NOT use safe mode and do not use that uninstaller
 
Download 306.23 again
Install it in Custom Mode, with everything unchecked but PhysX
be sure to put a checkbox in "Perform a Clean install"
 
That should fix you up

Find the NVIDIA folder on your C drive. Delete it. Then run the clean install option again.

What OS are you running?

#1 Download & Install Driver Sweeper & CCleaner.
http://www.techspot.com/d...66-driver-sweeper.html
http://download.piriform.com/ccsetup322.exe
#2 Click the start button, type in "change device installation settings" without the quotation marks into where it says "search programs and files" and hit enter. Change settings to "No, let me choose what to do" and "Never install driver software from windows update", Save Changes and exit. (Sometimes your older driver will want to reinstall itself after rebooting, this fixes that issues.)
#3 Delete NVIDIA folder from C:\NVIDIA.
#4 Run Driver Sweeper and Select NVIDIA - Display & NVIDIA - PhysX and click clean. Click No for Reboot.
#5 Run CCleaner and use the Registry Cleaner and Scan for Issues and then click Fix Selected Issues. (Backup the registry just in case something happens, CCleaner will ask you to do this after you click Fix Selected Issues.)
#6 Reboot your system
#7 Remove the following entries from add/remove programs... NVIDIA PhysX Driver, NVIDIA 3D Vision Controller Driver, NVIDIA 3D Vision Driver, NVIDIA HD Audio Driver, NVIDIA Update, NVIDIA Graphics Driver.
#8 Repeat Steps #4 & #5 & reboot your computer.
#9 Download the lastest driver from http://www.nvidia.com/Dow.oad/Find.aspx?lang=en-us
#10 Run the downloaded driver and select Custom (Advanced) Install.
#11 Deselect the following if you are not using them... 3D Vision Controller Driver, 3D Vision Driver, HD Audio Driver, NVIDIA Update. (Only things you should have selected are the Graphics Driver & PhysX System Software)
#12 Check mark Perform a clean installation then click next to install the driver.
#13 Repeat step #2 but change the settings back to "Yes, do this automatically", Save Changes and exit.
#14 Try opening control panel.

2013-July
I am here to stop all the time wasting and give you the straight up solution, No reboot, no uninstall reinstall :
1- go to services:  Run-> services-> enter
2- Change all the Nvidia services from " disabled" to "automatic"
3- start all the Nvidia services ( you don't need stereo 3d)
4- start Nvidia control 

I had this problem too but just updating to the latest beta drivers seemed to fix things for me.

xtrem_luka

2013-July
I am here to stop all the time wasting and give you the straight up solution, No reboot, no uninstall reinstall :
1- go to services:  Run-> services-> enter
2- Change all the Nvidia services from " disabled" to "automatic"
3- start all the Nvidia services ( you don't need stereo 3d)
4- start Nvidia control 

Thank you luka, though it didn't help me, it pointed me in the right direction.
Here's how: Do the same as luka said, then, (see below) Click on "Log On" and check to see that
                   "Allow service to interact with desktop" is checked.
As soon as I checked this item, closed Services, went to the desktop and tried opening
the Nvidia Control Panel, it opened right up. This is yet another hidden little item in Windows
that can really cause you some worry and a great waste of time.
I hope this works for you all, and that somebody will say what could've unchecked this box to begin with.
I know I certainly didn't.
 

 

xtrem_luka
2013-July
I am here to stop all the time wasting and give you the straight up solution, No reboot, no uninstall reinstall :
1- go to services:  Run-> services-> enter
2- Change all the Nvidia services from " disabled" to "automatic"
3- start all the Nvidia services ( you don't need stereo 3d)
4- start Nvidia control 

xtrem_luka its 2 years down the track and your assistance is still appreciated.  I had been searching for hours trying to get a solution and yours was simply the best!  
 
I wish there were more people who could just give you the simple answer that works!
 
Dude! You da legend!
 
 
Cheers
 
Xander78
 

if nvidia control panel is not opening then i would suggest you to first reboot your system then try again, usually every problem gets solved with this method but if this doesn't solve your problem then check the below methods.

1. run "msc", a service window will open, search "nvidia display driver services" open it and see if the start type is set to "automatic" and status is set to "start".
2. set the resolution to the high and then reboot the system, usually nvidia cp requires high resolution to open up.
3. uninstall and re-install the nvidia graphics cp, visit this link for graphic friendly approach .