Can't set IE window size

Hi all,

I'm having trouble setting Internet Explorer to it's maximised size. I had a rogue program installed on the computer and it changed several settings. Can't remember what it was called, happened 3 months ago. Ever since IE has been stuck in windowed mode. I've tried setting it to maximised under the shortcuts properties and that lasts for a few seconds after restarting the computer before flicking back to being windowed. Any suggestions?

Thanks.