Recently I tried to build PC by myself ,when I tried to plug in the 24 pin connector in motherboard, it was so hard,so I exert a lot of pressure and force on it, and I heard a tick sound after that. I am scared that the pins of it will be broken. What will happen if it's broken?
I think the motherboard would actually break before the pins would if it was like all the 24-pin I had difficulty trying to install. I had to hold up on the motherboard underneat where the 24-pin was to avoid breaking anything. Either way, the PC probably wouldn't work at all if you broke the motherboard or the pins. You can try to return the motherboard to the retailer or RMA with the manufacturer and hope you get lucky. But technically it wouldn't be covered under any warranty because it is physical damage.
You sure the tick wasn't it just latching? If you did break something best case it doesn't work at all, worst case you created a short which might melt some plastic or start a fire. Just watch it carefully after you first power on.
24pins often take a bit of force to get in with new hardware.
At this point the damage to the MB is done. Either pull the plug and check the damage or power up and see what happens. There is obviously a possibility it might not work if there is a broken pin, what kind of answer are you looking for?
Yes, it's possible something is broken and it still works. That doesn't mean it will function properly under all conditions. As you can see below, there are duplicate pins of each of the voltages (3.3v, 5v, 12v). If one of those lines has a break in it, you will have a problem when the system is demanding high power levels.