In most of the cases simply downloading the .dll file and then pasting it to appropriate place resolves the error. So first of all you should try this solution, search for .dll file from Google, download it and then paste it to appropriate folder.
If you are unable to resolve the issue by following procedure in step 1 then do this.
Try to restore windows to earlier date. To do this go to, Start, then Programs, then Accessories , click on System Tools and then open System restore.
Now follow the instruction given on your screen in order to restore windows to earlier date.
If step 2 or 3 is unsuccessful then the possibility is that some newly installed or uninstalled program have deleted the .dll file. In case you have installed a program, uninstall it to see if it resolve the error and if you have uninstalled a program try to install it again and when you want to uninstall it make sure you click “no to all” when it asks to delete system wp-content/uploads.
It is also possible that some virus is causing this error. Run a full virus scan on your system.
Try to update all of the recently installed programs and update your windows.