Sony released a patch earlier this week that caused a small number of PS3 owners to suddenly have a useless machine – as the main menu wouldn't appear after a reboot. Sony quickly pulled the patch but for some people it was too late. Now though, with a little bit of fannying around, it should be alright.
Those with unworkable consoles at the moment, will need to boot into safe mode (guide on how, here) and download the new 3.4.46 update from the official PlayStation site. Stick that on a pen drive and plug it into your PS3 once it's in safe mode.
From there simply update the firmware and you should be good to go. However if not, Sony suggests you get in touch with its support team. You can do that (and read step by step instructions for the firmware update) here.
The timing of this patch problem was unfortunate for Sony. It had been riding such a wave of positive feelings after its E3 showing, that this was a bit of a stumbling block.
KitGuru Says: Any of you faced with the near-bricked PS3 problem after that last patch? Hopefully this sorts it out for you.