Dynamic link library (DLL or .dll) is a set of small program files that are called upon simultaneously by various executable programs in Microsoft Windows to perform certain tasks like connecting to a device or saving a file etc. Sometimes, these files get corrupt and hence you need to register them again. You can register these files on your own. Check the steps given below and manually register DLL files in your Vista computer: (See Also Windows repair support)
Step1: Before you begin, make sure that you know the name and path of the DLL files to be registered. If you don’t know their names and paths, you won't be able to register them. Besides, you should take help of an expert if you don't know anything. It is because messing up with registry can lead to system crash or other severe problems in your Vista computer.
Step2: Click the Start menu> go to Run. If you don’t see Run anywhere, then press the Windows and the R keys together on the keyboard. This will open up the Run dialog box. (See Also Windows blue screen errors)
Step3: Type ‘regsvr32 C:\Windows\System32\Name.dll’ in the blank field (without quotes and as it is) and then click OK. This command is intended for the example. You must replace the path as well as name of the file (Name.dll, here it should be the name of the file with .dll as the extension and not just Name). For example, you have your files stored in H:\ drive and not in C:\ drive, then you would type regsvr32 H:\location of the file\name of the file followed by .dll.
Step4: Once you click OK, a dialog box will appear showing that the file has been successfully registered. Click OK to exit this window. If the program did not launch automatically, then open it manually. (See Also Windows Vista support here)
Step5: If you get an error message like the specified module or entry could not be found, then it indicates that you are either typing the location or file name wrong or the .dll file that you are trying to register is not compatible with your version of Windows.
Step6: If none of these is the case, try disabling the UAC (User Account Control) in Control Panel. You may need admin privileges to run such command or tweak the registry. You can also download and install a free or paid tool from the Internet to automatically install missing libraries or fix common problems. (See Also how to fix registry errors in Vista/7)