It sounds like you have an inverter problem. I’ve had this popup with several older Mac Powerbooks. It’s cheap to replace the inverter but a pain to fix. The inverter is inside the display itself, so you need to take much of your Mac apart to get to it. Make sure you get the correct inverter for your model. Apple tends to change parts with each new iteration of its computers, so the inverter is specific to the Mac. Once the inverter is installed, however, your screen should work well again. Update (10/31/2018): OK, sorry to bother you.
In most cases, third-party lens makers (Tamron, Sigma, Tokina, etc) must reverse engineer lenses to make them work with Canon, Nikon, etc. cameras, which means they don’t have direct access to the latest from either of the camera makers. What all that means is that a lot of times, you need the same generation lens as camera. For example, I have a Tamron 70-300mm f/4-5.6 LD Macro AF lens for which I paid $29 just for fun. The “softness” of the low-end lens actually makes it ideal for shooting flowers, specifically with my older, lower end Nikon D70. The lens works perfectly with that body. However, if I put the same lens on the older Nikon D100 or newer Nikon D800E, it has trouble focusing sometimes, and hardly ever does it in live view on the D800E. The ideal solution is to look for a third-party lens made around the same time as your Nikon D5300 (2013-2014) DSLR camera. The good news is, such a lens will be cheaper than buying a new one. Hope this helps!