Start up a system monitor (System Information, or top/ntop/htop, or Task Manager, etc) and look at what is going on. Is your CPU active? Are there any disk writes? Is there any swapping or paging?
* If the CPU is high then the program is still working. Small chance of something broken.
* If the disk is moderately active the program is still working. High activity is not a good sign and suggests some fault.
* If there is a lot of swapping then your machine is thrashing. It is spending more time swapping than computing. Kill the process, kill all other apps, and try again. You may even want to reboot.
You can also open up all the temp and working directories that PI uses and check the file modification times in there. If you find any file or directory with a current time then the program is still working.
As a general rule, a program that shows no progress after several hours is stuck. Stop it and try again. If you get stuck in the same place, then there might be a real problem.
Note: I am assuming that you have done this successfully before, that you have not changed your OS or app versions, that you have not installed anything else, and that your machine has not been changed at all. And I am assuming you are using data files from the same camera and a similar number of exposures as in the past.
Which reminds me of an amusing anecdote. I was once asked to fix a bug where the customer's software froze up on a particular dataset. I spent a week tracing the block to a sort routine supplied by the OS, which had me pawing through the OS code looking for changes (we had a source license) and drawing blanks. One day I was down in the machine room (it was that long ago) and over the noise of all the fans and industrial AC I heard the disk drive. What the hell? I ran a system check then looked at the size of the dataset. Then I stormed into my boss's office.
me: this file is 100 times larger than normal!
boss: the customer decided to consolidate their paper trail. They used to run each sales counter separately and now they run them all at once. There are 160 sales counters.
me: I can't fix this! It would take 100 times as much memory and 1000 times as much time! Tell the customer to stop doing that!
My boss didn't want to tell the customer that. But he finally realized that even "the customer is always right" has to bow to the laws of physics. I parted ways from that company soon after.