Portal 2 isn't working

[Jarl Løngsteppy]

So, a while ago i downloaded portal stories mel and after i di that my portal 2 stopped working. i ignored it at the time but now i rly want to play. what happens when i start the game is the scren goes black (normal) then it stays black for about 45 seconds (not normal) then my desktop flashes for 5 seconds (not normal) and then it goes back to the black screen and then the game closes and a steam pop up says "Failed to create D3D device! Please see the following for more info. http://support.steampowered.com/cgi-ban/steampowered.cgf/php/enduser/std_adp.php?p_faqid-772" when i type that it it says the page wasnt found. Can someone help?

[cheshirm]

google "steam failed to create d3d device" returns
https://support.steampowered.com/kb_article.php?p_faqid=772

[Jarl Løngsteppy]

I'll try it thx