os: Windows 7 ultimate 64 bit sp1
cpu: AMD phenom II X3 720 2.8 Ghz
graphics: ATI radeon HD 5770 1gb
Ram: 8GB ddr2

hi, yesterday I bought gears of war pc through games for windows live marketplace. I'm having trouble getting it to work

I've been around the forums looking for fixes, I've seen a lot of places saying I must patch the game, (this being distributed digitally I assumed the patch was preapplied) so I downloaded the latest patch and attempted to patch
I then got the error for "old file not found"
So I googled this error annd everywhere I go theres people saying you need to not used a cracked version of the game or copy the startup.exe from the disk. . . well I dont have a disk I downloaded it from the marketplace
so patching seems to be out of the question which leads me to being out of options really

so I'm posting here
ok what happens, the game loads up to the main menu just fine no problem, however when I go to the campaign and start a new campaign the opening cut scene will start, there will be a black screen for about 5 seconds and then the screen will flicker and I'll get a "gears of war has stopped working" box
I've tried multiplayer and that seems to work however I've not found any games yet so I cant actually get into a game with less than two people, which is a shame because I just wanted to roam the maps to see if it works.
I've looked around and there doesnt seem to be anyone with this problem, and I dont want to uninstal it and re download again because I've done that twice already.
I spent ú15 on this game, and while I do have the xbox versions of all three gears of war games I wanted to play the pc one, and right now I'm very disappointed
any help would be appreciated