Go to your settings in xmb, then "system settings" then "system information". That will tell you how much GB you're using so far on the HDD.
As for your problem, also under system settings there is an option called "restore default settings". try that, (you won't lose any data) Though you will lose all book marked sites in the browser.
Not a sure fix, though something to try.
MyPS3 Miscellaneous
1 day / Sydney Northen Beaches, The Watcher