TDR Failure atikmpag.sys + vertical lines on screen
I have a Sony Vaio SVE171E13M notebook with Windows 8.1 and I am having problems with this error. I tried updating the driver or rolling it back but it doesn't work,whit the AMD driver Windows won't boot, it will keep crashing, without the driver it will boot but it shows me that there are only 256 mb graphic memory available. Also I tried replacing this atikmpag.sys file but when I reach in Command Prompt the "chdir desktop" step says that he could not find that path. I tried uninstalling all the amd drivers and installing them again.
Can anyone help me step by step with this issue? I want to mention that I'm not a computer guru so please have patience with me also,sorry if there is annother post with this problem and I didn"t see it, if that"s the case please give me the link with that post.