If it is Windows 10 and it is trying to apply the Creators Edition Autumn Update (1709), then it took my PC about 5 to 6 hours and three separate attempts before it worked. It also downloaded around 8 GB during the three attempts. I have a 70 Mbps download speed, but if yours is much slower, then it could take longer.
I found that on each attempt, it eventually said a restart was needed. On the first two attempts, after the restart, the update history still showed that a restart was needed to finish the update, even though it had just had a restart. On the third attempt it worked.
Be warned, several of my settings were changed from the way I wanted them to settings that Microsoft wanted. It took me about an hour to go through all the settings and correct them.
If the PC is still allowing you to do things, leave the update running and use the PC as normal. It might be a bit slow, but you should still be able to use it. If neither the keyboard or mouse (or whatever input devices you have) will respond, even if you wait for some reaction, then the PC may be completely stuck, in which case all you can do is shut it down and try again. The clicking sound suggests that it is still doing something with the disk drive, which means it may be progressing slowly with the update.
I think my PC appeared to get stuck at a certain percentage for a long time before eventually moving on, but I wasn't watching it all the time. I can remember one period of about half an hour when it hadn't moved, but an hour later it was ready for a restart. As I wasn't watching it continuously, I don't know just how long it waited at that one percentage.
I have seen several reports of problems like this that Microsoft have caused with their Autumn Update.
I hope this helps.