LEDs for a computer

Im trying to add leds to my computer and have a tactile button next to my computer power button so when I turn it on the lights turn on as well. I don't know anything and conmpletly new to this, so I was wondering if anyone knew how I could make that possible.
I was also wanted the leds to turn on at different times and turn off after around 3 seconds without pushing anything is that also possible?

If you have a spare 5V connector from your computer's PSU, you can connect your circuit to that. Then it will switch on and off when you switch the computer on and off and you will not need a separate switch.

Yes, you can do all sorts of animations with the leds if they are controlled by Arduino.

Tell us more about your ideas and we can suggest components. How many leds, what colours, what animations and so on.

Oh ok then I will have to look into that when I get home.

If you’ve ever played overwatch I want the animation to look like reaper’s ultimate which is basically a barrage of red gunshots everywhere. So basically red leds going wild and then in 5 seconds or so turning off.

If you've ever played overwatch

No. You will need to describe what you want to achieve more precisely. How many leds?

I can’t explain as well as I want to but basically I want it to look like red lasers are being blasted at fast rates
If you want a visual idea look at this video and skip to 3:10

As of how many leds I was thinking of using the flora smart pixels because I can separate them inside the case and choose the areas they light up but i don’t know if it’ll work outside of a fabric area

OK I think I get the idea.

The pixel leds would be a waste if you only ever use red, but perhaps you can illuminate the pc case with other colours at other times. Not sure what you mean by “fabric”. HOW MANY LEDS???

Yeah that does make sense not to waste them like that and fabric because that's all I saw the flora used with.
I was thinking of using 20 leds maybe even more

Well, for the effect you want, you probably need only some of the leds to be lit at any instant. You could use "ordinary" high brightness red leds, connected electrically speaking as a matrix. For example a 6x5 matrix would allow you to have 30 leds with one led lit form each group of 5 at any instant and be able to fade them out for a more convincing effect, then switch at random to another in each group. Stagger the fading between the groups and you should be able to get something like the effects from the video.