imac 27" graphics card late 2009

Hello,

I am facing serious graphics issue in my IMAC 27"

below is my specification

initially vertical Strips are showing on boot. and then after few months it wont boot to login. hang in start up with blank screen.

then i bypass graphics by following this steps( https://people.cam.cornell.edu/~zc227/extras/early2011mbp_graphics.html) but experiencing slow performance. but works

I need to know

1. can i upgdrade the graphics to 1/2 GB ? card ? if yes then which card ?

2. how can i increase the performance or fix the graphics card if possible ?

need expert advice please help!!

最後更新：2017-09-12 16:17:04