I am using lightroom 5 and my camera is a pentax k5 ii shooting in RAW (DNG) with sRGB. When using a vignette, banding/lines occur and have not had this problem before.
One thing i have changed is my laptop which is now an ASUS N550JK running the full works (i7,16GB RAM etc)
Please help solve this issue.
The amount of ram is irrelevant to your banding issue. Your new screen may indeed be the culprit. Depending on how you've calibrated it (or not) it may not be capable of displaying a smooth gradient. See if you can look at your file (at 100 percent magnification) on a known higher end calibrated screen and see if the problem still exists.