Sony Takes a Mulligan, Issues New Firmware to Fix Bricked PlayStation 3 Consoles
If you tried installing last week's firmware (version 4.45) and can no longer see the XMB (XrossMediaBar) menu, Sony says you must perform the update to version 4.46 by starting the system in safe mode. Sony set up a page with detailed instructions on how to do that.
For everyone else, you can install the 4.46 upgrade as you normally would. The new firmware is supposed to improve system stability and also adds an option that will allow you to hide notifications when you earn a new Trophy. Otherwise, it's a mostly uneventful firmware upgrade.