Default screen blacks out and wifi drop outs

Not sure what wrong with my Prime,
1.
It has been dropping strong wifi sites on a regular basis for a long time. It will connect ok but if I let it go to sleep or change apps it will usually drop the connection. Have set power settings not to drop wifi, but that makes no change. No idea what is the problem.
2.
When using the built in library app and changing pages in epub book the screen will sometimes go black and wont come back on for a minute or 2. Sometimes it happens when rotating the screen. No idea?

It is rooted but using the OTA standard ROM.