The first thing you will have to check, when the dll error occurs is whether the error is caused due to a missing file or a corrupt file or due to a file with a different version.
First, run the following command in run dialog box (just copy and paste it in run dialog):
This will restore corrupted files but it is not guaranteed to give complete solution at all costs.
After doing the above, if a dll file not found error occurs, then there are a lot of secure websites where you can download dll files. Just Google for them and you will get it. They will mostly come in zip files containing readme files containing information where they have to be pasted. Some even come with registry keys for registration purposes. Merge the keys if needed.
Note that this is similar to a first aid mechanism, which might not produce a complete fix. Sometimes copying a dll file with a wrong version may also result in increasing the problem. But this is a good start in handling dll errors.