"The server encountered an internal error..."

[Connie]

There is so much information here in the forum about possible reasons why this happens
so a "me too" is not helpful to find a explanation for your situation

"don't know for sure yet." how can we know?

1) there is a check when you install, did you check that everything was ok, that all requirements for GS are fulfilled?

2) you could tell us which server, PHP version etc. is active

3) did you activate rewrite mode and nice URLs?
4 .. more questions possible

The best solution which takes only 5 minutes:

0) CLEAR your Browser's cache
A) DELETE the complete installation at your host!!
B) RE-UPLOAD the uncompressed GS version to your host
C) RE-START the installation AND take note of the server check which is run at the beginning of the installation process
D) ONLY continue when everything is ok
IF NOT ask here or your hoster's support
E) CONTINUE STEP by STEP and take care what is going on, not only clicking OK