Iphone 4 apps keep crashing

I have an iphone 4 and over the past couple of weeks some of the apps have started crashing, not all of them, but around half, including most new ones i download. At first i thought it was because the memory was almost full, i cleared out the phone and now have around 4gb free and it is still happening, i also always make sure i end the apps i'm not using and it still happens.

it's very strange, for example i can open my twitter app and browse tweets for as long as i like, but as soon as i go to compose a tweet the app will crash, also facebook and most games do this. Even the built in mail app crashes most times i open it and the screen goes black and the phone restarts sometimes. Everything is up to date and i'm clueless as to what it could be.

Restart your phone
plug it in to your computer
open itunes
press the home and power button on your phonne at the same time
count to ten
let go of the power button but keep holding the home button
go to itunes on your computer and restore your phone

then your phone will turn on it will be as if you just bought it (note, this will erase everything)
i don't know if it will work but probably erasing everything and getting it as if its brand new will work