Issues with all video formats.

Hello. (sorry if there are any mistakes in my English )
I have problem with video formats in all DaVinci Resolve versions. The problem is when I put a video in the timeline it is either laggy or it has no sound. I'm using two video formats MTS and MP4 and none of them are working. I also tried rendering it and after rendering i still had these problems.
Do anyone know how i can fix this in Resolve 16.2?

My PC specs:
CPU: Intel x5650
Graphics: NVIDIA Quadro 4000

Laggy can have many explanations -- incorrect settings, timeline and media resolutions which exceed the system capabilities for real-time playback, lack of GPU acceleration (in the case of the free version), difficult codecs, etc. Both your GPU and CPU are weak, by current standards. Neither would be recommended today for Resolve.

No sound can mean the embedded audio format isn't supported. mts files often have AC3 audio, which the free version of Resolve can't decode.

With your current system, you'll probably want to use "optimized media" (covered in the manual) and you'll likely need to transcode the clips with AC3 audio to another format, with a third-party program like Shutter Encoder.

your xeon has no quicksync for H264 codec
and the 4000 is very very outdated

if it is a 4,1/5,1 classic mac pro, upgrade to X5680 or X5690
and have a look for a sapphire pulse RX580 8GB GPU
and with opencore (from mojave up) you will get HWacc for H264 and H265
on the RX580