Also, in Safe Mode with Networking try configuring the computer to "clean boot":
http://support.microsoft.com/kb/929135
Follow Step 1 to clean boot and then see if you can then log into Normal Mode.
If that works there is further troubleshooting in the article to try to find the cause. Step 7 will return a Normal Startup.
Also, there is a tutorial in the following link on setting up WinDbg of the Debugging Tools for Windows, such as setting the symbol path and utilizing the !analyze -v command:
http://www.sevenforums.com/crash-lockup-debug-how/26584-2-intermediate-configuring-debugging-tools.html
Basically, install the Debugging Tools for Windows, open WinDbg, > File > Symbol File Path and then paste the following under "Symbol path":
SRV*c:\symbols*http://msdl.microsoft.com/download/symbols
then click "OK"
Then close WinDbg and answer "Yes" to the "Save information for workspace" question.
Now open WinDbg and drag a minidump file onto the WinDbg GUI or WinDbg > File > Open Crash Dump > then browse to and select a minidump file.
To get more information on the crash, type the following at the kd> prompt, and press "Enter":
!analyze -v
To get a list of drivers loaded at the time of the crash run the lmtn command at theKD> prompt.