Download the zip version from here:SourceForge XAMPP File Repository
Copy over the missing files.
Or do a complete reinstall using the zip/7zip method in this post:viewtopic.php?p=179699#p179699
which might be the best idea because you are still at the early stage of installing 1.7.7 - but be careful what you use to extract the 7zip file as we found an issue that fails to extract zero length files, which seems to be your problem and XAMPP has many zero length files that it uses to function correctly:viewtopic.php?f=16&t=48955
I hope this post is more helpful.