Graphics glitch?

[MarkofZollo]

After downloading from steam on saturday I have had constant problems, starting with seeing the desktop only when in mission, not sure how I solved but since then pathetically low fps anyway. I have tried most solutions and even on low and windowed I barely reach 30 fps with occasional choppy movement over sea. I have noticed that everything outside the cockpit seems to re render textures constantly which may be the cause of problems as fps drops during this, anyone else notice this or know how to sort it?
On low and medium settings its a worse looking game than the last!
Funny from other posts I reckon this would play better on my Mums low spec pc.
(Btw 2.5Ghz Q9300 on Asus mobo, 4gig 800Mhz ram and dual 8800gt, nothing overclocked just ran Crysis 2 on top spec! - disabling sli hasnt helped)

Additional: After doing camaign first mission and pressing esc as asked, it says I failed the mission when in game said I completed? Have not found related solution so thought I would add to above.
Thanks for any help!