Glad I could help, just frustrating that I didn't figure it out sooner! :D

Same problem. Numlock not helping. Would really love to play this game I paid for.
Playing on Windows 7 and nadda.
Opens, get to a screen where * is my name, click, and loads a blank page.
Very dissapointing.

I know its been a while since this was posted but I was having the same problem and thought I'd post my solution.
My laptop doesn't have a numlock key so I was at a loss. When you get to the nickname screen, try pressing fn and enter at the same time. ^.^

That's what worked for me~!

Ive got this problem but my laptop doesnt have a numberlock button...What am i suppost to press instead :/

Somehow it looks like the problem is some keyboards sending the wrong "enter" signal. There's a way to rebind it so that it uses the right one.

Install Sharpkeys (http://www.randyrants.com/2011/12/sharpkeys_35.html). Run it, and click "Add".

Click the left "Type Key" button, then press your "Enter" key. You will see some key ID (when I press my usual Enter button, it appears as "Special: Enter"; when I press the one on my number pad it appears as "Num: Enter"). Click OK on this. Then, on the right-hand side, scroll down until you see "Special: Enter".
Click OK. Your selection will now appear in the main SharpKeys box. Click "Write to Registry", and it will commit the change (don't worry, this is completely reversible)
Click Close, and reboot your machine. Now your Enter key will be seen within Windows as a regular Enter key, and not whatever it was bound as before - and so it should be accepted by Theme Hospital.

If you want to undo this change, just start up SharpKeys again, delete the binding from the list (choose it + Delete, or just Delete All), "Write to Registry" and restart again. This will remove the new keybinding entirely.

Hope this helps!