Yellow lines on my screen+crashes?

I would try a System Restore which reverts your computer's settings back to a previous state. If you know a time when your computer was working properly, you can try System Restore, and if it does not fix the problem, it can be completely undone. The restoration will not affect your personal files or any files that you put in the My Documents folder (at least in Windows XP, double check this for Vista) however it will delete any programs that you installed after the chosen restoration time (unless they are in My Documents). In XP you find System Restore in Programs>Accessories>System Tools>System Restore. You should be able to access it in Safe Mode.