Here’s how I CHMOD…
1) Use WS_FTP LE (type it in on Google, download it for free)
2) Enter in your ftp server details, pretty self-explanatory
3) Once connected, browse to the directory containing the folder or file that you want to modify the permissions
4) Left click the file/folder, then right click and choose “chmod”
5) Tick the appropriate box, hit OK.
Done.
I had this problem, althought I could login to the admin section and all was fine.
Try making sure that your wp-content/themes folder is readable, by CHMODing it. If it isn’t readable, wordpress won’t be able to render up the posts requested from the database.
Hope it helped.
Tom