Texture problem and crash issue

Hi, I'm Using XNA and Gamestudio but for some several reasons, I'm searching for another solution. I installed unity and had some problems just from the start. Whenever I run a project such as the demo island, I can see the texture lines and in some seconds the game had a crash with the issue of vista: R300 had a serious graphical problem but windows succeeded to handle it. It gives in every 2-3 seconds after the first crash if I still don't stop the run process. My computer is an optimised x64 for graphic design and programming with stable devices in it. Using Vista and working well with the game engines I develop or any other populer graphical solutions. I searched in forum but can't reach an answer. And the wireframe problem also can be seen from the island demo which can be reached from the unity site as the webplayer feature. I guess the crash and the wireframe appearance are related. Thr bug report option was appearing on the start but I chose to give it a try more to understand the frequency but for now the bug report is not appearing anymore so I do not have a bug report number. Can someone tell me how to fix the crash and the wireframe issue? Thanks in advance

after i searched everywhere and installing all the drivers and windows 7, i opened my desktop and saw my graphics card fan is not working! Now i changed it and all the problems disappeared. High temperature causes those problems if anybody will face with the same issue.