You have reported that Vegas cannot open a file and have not told us nothing about that file. A report from the free MediaInfo utility would be useful.
I'll bet you are paraphrasing to us what the error message is telling you. In one message you said the message was a problem with a codec and in another the message was an error opening the codec.
I'll guess that your file is probably an AVI, or maybe a Quicktime file and you are missing the necessary codec to read said file.
Another way to have a problem with a codec in AVI and Quicktime when it is installed, is if the installation has been corrupted.
As previously stated, the free MediaInfo utility can inform you of the contents of a file.
With AVI files, free utilities like Gspot can help figure out AVI codec problems.
If the file is a Quicktime MOV file, then make sure Quicktime (QT) is installed. If QT is installed then make sure QT can play the file. If QT cannot play the file then Vegas will not be able to use the file either. Solve the QT playback and then Vegas will probably work with the file.
thegriffin88, you can't expect the "doctor" to diagnose and fix your problem unless you believe in magic, voodoo, or at least accurately describe the symptoms and answer a few simple reasonable questions.... or why bother to come to this Forum.