Okay so the situtation, im using or used 14, 15 pro, the problem when i editing and chopping some parts and trying playing preview or seeking totally lagging, permanently working with shift+b method , BUT this was worked before normally without lag, now not, whats the problem?

My op win10 x64 (fresh install, no virus/malware), ssd +2hdd, vga was on service and no problem (gtx 1060 6GB), ram not because runned memtest and no errors (2x8GB DDR3), cpu fm2 amd 740 4 core (yesterday changed for testing with 2 core but more sh*tter :D )

So looks like cpu or motherboard problem?

Note i cleaned the AC part, maybe try again connecting the cables?