The first thing to try with "serious startup error" problems is to
- restart the computer,
- press the SHIFT and CONTROL keys,
- keeping SHIFT and CONTROL down, launch Mathematica,
- release SHIFT and CONTROL when a Mathematica window opens.
If that does not cure it, and you had another Mathematica (Trial, 7.0, ..) on this computer before, search for the "mathpass" file and delete it. You will need to search Hidden Files and Folders.
If those does not fix the problem, try creating a
folder through the Windows Explorer (or from My Computer). There might be a permissions problem. Did you install Mathematica as a user with Admin privileges?
Last simple test: remove Mathematica (from Add/Remove Programs control panel) and re-install it.
If none of the above fixes it,
a) try starting the Mathematica Kernel by itself
(Start menu - All Programs - Wolfram Mathematica - Mathematica for Students - Mathematica Kernel).
b) write to firstname.lastname@example.org sending
- whether the Kernel works by itself (and any error messages that appear),
- screen shot(s) of the error(s) that appear when you launch the main Mathematica,
- if you can, the output from running systeminfo in a command-prompt window.