My Iphone4 can't restore (error 21)?

My cat dropped my iphone cause it jumped on the table and I guess she just kicked it while going up, and it fell (It's like 2 feet high). I only had it for 2 weeks and I had a case on it that's pretty secure and i'm pretty sure I don't need to replace it or anything. When it went on recovery mode and I connected it to itunes, and when I tried restoring it, it just keeps saying "The Iphone could not be restored, An unknown error occurred (21)" I tried changing the hosts file, using tinyumbrella, disabling my firewall and antivirus but it still keeps showing the error message. Please help me? I'd appreciate it, thanks in advance.

Check this on the Apple Forums - a loose or broken battery can cause what you're experiencing, which would make sense given that it was dropped.

https://discussions.apple.com/...0&tstart=0

For the future, think about getting an Otterbox - I've got one for my 4S and dropped mine many times from much higher than that onto concrete and other hard surfaces without any problems.