have patience man,i finished the game same on xbox360 and on pc,i can say that its harder on pc with the keyboard but it can be done.remember PATINCE
boy getting the 6th seal really tests ur patience. i was almost at the end of it when like a freak accident it all came together and i had the 6th seal. but after all those hours and all those attempts..it was truly worth it.
There are six seals, all of which can be located in your inventory unless you already planted them for the armor (so you know how many left you gotta get). I found the tomb runs to be rather easy imo, some I failed for the first couple tries but once you understand what to do. Rest is pretty easy.
If you haven't gone for this yet, you have to. Even making it a priority. The armor set is kick ass. Best in game actually, theres just no comparing it and it's free.
don't get me wrong..the tomb runs were easy and a lot of fun with a lot of fluid motion..but getting the 6th seal is the most difficult..some of us feel it is ridiculously difficult. but in the end its worth it.