I been stuck on sader songs

Since I have been fighting stage 4 cancer I have noticed my music of choice is hardcore, or about letting go and living life. It actually drives me nuts.

I'm sorry you're going through that in your life right now. You are pretty insightful, to have noticed that your recent music choices reflect your current mental states.(I wonder if you are becoming more introspective lately, living with this fight for your life?)
I can certainly relate, with the music choices we make appearing to reflect our current mental state/views at any given time.
But did you know that your mental state can reflect our music choices as well? (Probably. But I just point out the obvious, because...)
I've found that this can be an unhealthy addiction in a way. I've wondered if it's possible to be addicted to sadness, or at least the feeling of "melancholy". It's deep, beautiful, and all-consuming... It can actually be a crutch, and it's important to be aware of the impact that your listening choices has on your mood.
It's known that our brain literally absorbs the things that we expose ourselves to, or are exposed to from our environment.
Basically, what we take in, is what our brain puts out.
Think of it like, seeing negative images on the news all the time = people relate; feel more negative.
Likewise, hearing a sad song about hopelessness = people relate; feel more sad/hopeless.

Give yourself a break and try listening to happy music. Even if it doesn't give you that same satisfaction--even if it even creates a sense of cognitive dissonance, where you hear the music and automatically RESIST allowing yourself to enjoy it because you THINK you can't be happy or relate with something that feels so foreign to you at the time.

I'm trying to do the same. It's hard and sometimes I find myself zoning out and actually just ignoring the happy music (or happy videos I try to watch); sometimes I just struggle too much to focus, and my thoughts are stuck on the depression.
But today I noticed that I can focus on happier things for longer, and am thereby focusing less on the sad things. I assume it will only keep better, and I hope that things will get better for you too, OP.

when i feel down,linkin park song with me.i feel more movtivation .and the song are meaningfull.talk about life and human.

It is very sad that you have cancer, I hope you get better. You can try with sad piano, there is very good songs.

Sorry to hear about you having cancer my bro, but you can always try some older songs as in country or Elvis, beatles etc. These all get me into a good mood, give it a try