Question: I've installed TFS 2008, but I can't seem to access the server. When I try to connect to it in Visual Studio, I can't. If I try by browser on a remote PC, I get a generic page cannot be displayed. On the server, I get a 403. Nothing was touched in IIS and the service is running as a Network Service. Any ideas?

Answer: 
try:

<http://localhost:8080/Services/V1.0/ServerStatus.asmx>. This will tell you if TFS is up and running. If you are getting anything else you need to look into IIS issues.
I went through everything on a similar problem.

I logged onto my tfs server and connected directly there.

I also used a TFS admin tool I downloaded some time ago from Microsoft, and made sure I was in all the right groups and projects.

I then went back to the client PC with the problem, tried the services/1.0/serverstatus.asmx?op=CheckAuthentication Url again, and it worked this time.

AFter that full service was restored to my PC.

So I don't have the exact answer, but I would go through the checklists presented by Grant Holliday in his answer.