I don't see anything odd. I see a forum with a default theme and thousands of posts. It sounds like this may be browser-dependant or conditional. Check the integrity of files, such as index.php using the File Verification tool in the ACP.
PGP Key (Fingerprint: 23B6 F4C0 FE2D 45AA 61A0 1E86 DB87 09DC DD87 6E40)