I did not point you to any codec download. I pointed you to a tool that allows you to manipulate your system's existing codec settings. You still haven't specified exactly what you did. Since I have virtually no information to work with, I'm afraid I can't offer further suggestions at the moment.

I have downloaded this codec "K-Lite Codec Pack Basic 10.4.5".

> I have downloaded this codec "K-Lite Codec Pack Basic 10.4.5"

It's not a codec. It's a codec *pack* (many codecs bundled). And unless you specifically tell it to use an alternative codec (during setup or by using one of its configuration tools) -- specifically DirectShow filter -- for WMVs it won't change anything.

What codec should I use?

Try different ones and see if any of them improves the situation.

I have tried finalcodec and other codecs. It doesn't help. It is really weird that both the video and the slider bar flashes. Even I have downloaded the perfect codec, it cannot solve the flash of slider bar. I give up.