Open with & application not found msgs

Hello,

I'd really appreciat it if somone could help with this annoyuns- earlier today i tried to get on the net and then i i had loads of msgs saying your computer is inffected with a trojan or melware. And so didi a system restore. as soon as i did that every program i try to open it comes up with appliaion not found including the help & support option won't work anymore.

NB: Not that great with computers so would need a detailed solution...(step by step plzzz)

How do i get my pc working properly and what can i do or download to prevent this happening again?


thank sooooo much