Samsung Galaxy S II :: Booting Taking Long And Several Applications Not Working Anymore

I have a SGS2 that is one year old, I still use gingerbred 2.3.3, and I haven't attempted anything special prior to getting the problem. I first noticed I had a problem when I booted my phone yesterday: booting took much more time than it use too, but then it worked. After entering my password, I got access to the usual page, but then, pop-ups appeared one after the other saying: "Sorry, need to close the application "name it". Thanks for trying again" (don't know what's the precise wording in english because mine is in an other language... still, you get the picture). The phone still works for calling, SMS and a bunch of apps... but applications like facebook, twitter, lookout, dropbox and a few games won't boot anymore.

Other things I noticed:
- I lost a few apps (at least 2) that disappeared completely from the phone
- I can't erase the cache when accessing settings/storage. Also, it won't recognize the SD Card space availability in the storage section. However, when looking at it by accessing settings/applications/memory usage, I can see what are the apps on my SD card.
- There is no correlation between the apps that have problems and the ones found on the internal SD memory card.
- Over the past month, my phone would sometime reboot after being closed. Didn't happen frequently, but I read this could be linked to the USB port? Anyway, just saying it here while I'm typing something.
- Finally, I have the feeling the OS version is not the one i had previously (downgraded?) because several apps asked to be updated after rebooting the phone a few times. Just I feeling because if i changed the OS for an upgrade, it was over 10 months ago.

So that's it. I already tried booting with the three buttons trick to erase the cache in basic mode: didn't changed a thing.