How to record a video directly in my computer from my nikon d3200?

I have to record a long video and my memory card won't do… So i want to record directly to my pc

No.

If you want to record long video scenes, you have to use an actual video camera

Nikon, Pentax, Canon, Sony and others make still camera which happen to have a video feature, but they do NOT replace an actual video camera

That said, the upper range Nikon's like the Nikon D810 and D4 series cameras can record directly to a hard drive using the HDMI port on the camera. Since your D3200 has an HDMI port, you may be able to record video directly to a special hard drive designed to record video via an HDMI connection, but you are going to have to do some of your own, independent research

No you can't do that.
Not only is there no easy way to get the signal to your PC, but even if you find a way around that you will also have a problem with the camera.
Your limit on the memory card is driven by the file system having a maximum file size of 4GB that equates to around 12-20 minutes of HD video depending on resolution. Your PC will have a different file structure and will allow bigger files but your camera sensor will then become the limiting factor. The camera sensor will overheat and shut down after around 40-60 minutes. You also need to consider battery life - my Canon 70D eats batteries in video mode - I guess your D3200 will not be much better. Around 30-40 minutes max on 1 battery charge.

You have 2 easy options:
1. Buy a Camcorder - they have no file size or overheating limitations - 32GB card holds 3-4hrs medium res HD video on mine. Cost around £$€250 for a reasonable camera. My Canon Legria HFR36 gives 3hrs operation on a high capacity battery, A little more if I turn down the brightness on the LCD screen and as long as you want plugged into the mains with the adapter in the box.
2. Buy a high quality HD webcam - cost around £$€50 and record direct to your PC. The only limit will be the size of your PC's HDD

No DSLR or stills camera can "record a long video".

Because the maximum file size for video files on the memory card is 4GB. Which means the maximum clip length is around 12 to 20 minutes depending on the video format you choose.

If you want to record video continuously, then you need camcorder.

And if a D3200 is what you have and not budget for more cameras, get more cards. You can't do one continuous take anyway, and you will just have to do video editing. There are not many hours-long unedited videos that anyone would want to watch.

Wow, cameras have changed a lot since this thread. It is simple to now record to SD card over 30 minutes or for cameras with a limit just record directly to PC/Mac via a mini HDMI to HDMI into OBS.