Sony have released the 2.41 version of PlayStation 3 firmware. This version is supposed to fix the errors from the previous version, 2.40.
For updating the firmware, you just have to turn on your console and go to "Network Update".
"As many of you know,
we released PS3 firmware update v2.40 last week, but had to take it offline
temporarily because, for a limited number of users, the XMB wouldn’t display
after the update was installed. We’ve been able to fix the problem..."