Safari not installing extensions

Today, I tried to install Stylish, a safari extension, and every time I tried to install it, it wouldn't work. I'd click on the plug-in from my downloads folder and it would open up the 'top sites' / blank page.

So, i tried a different extension, and it does the same thing.

I also tried putting it in through the internet plug ins folder, and restarted, and it still didn't work.

I tried installing Stylish via the apple website, also didn't work.

I'm on Safari Version 7.0.5 (9537.77.4)

OSX Version 10.9.4

I also tried to re install OSX but it didn't seem to work properly, so if there are no alternatives, I'll have to try re installing again and I really don't want to have to do that. Thankyou

(If i've categorised this wrong or missed anything out, my apologies)