Are you installing as Administrator? Windows 7 appears to have a number of processes that need to be gone though to ensure that a non-Microsoft product is installed properly, even by an Administrator.
Make sure that permissions have been fully and correctly set for every folder created.
Has User Access Control been disabled while trying to install?
Has IIS been turned off if it is turning on?
A lot of installs appear to be being stopped silently by Windows 7, for security reasons of course. Windows 7 has been locked down so tight one can only assume that Microsoft does not believe anyone really knows what they want on their computer, unless it is a Microsoft program, of course.
If you had a Moodle trainer install and set up your Moodle, how was it done? Is it a Xampp installation or a Standard install? What did he do to get it running? Can you ask him?
<rant style="rant-type:disgust">
The big question for me is why would anyone install your Moodle for you without doing it with you? Would it not be a better training option to go through the whole download and install process so you could replicate it? To not do that is, for me, intellectual dishonesty, which leads to frustration for the trainee when they want a variation - ipso facto - the discussion above.
</rant>