This one is tricky, I already scanned with antivirus and that doesn't seem to be the problem (? but iI don't really know for sure either).
Something I did has created this problem. No matter what the document's title is; no matter if I change the name of a document and save it; the next time Word opens the "Save As" dialogue I see the same string of the name I gave a document days ago. I can change it to save my new document, then close Word, or even also turn off the PC. Then when I open Word and try to save another document, the "Save As" dialogue again defaults to the document saved days ago. It's always the same name. Although it's not the end of the world, it is anoyying. I tried and erased the string from the registry, then it appared again in the "Save As" and this time I wasn't able to find it in the registry (but this I will retry just in case I misspelled the string.) Any idaes?