Freezing up

just got a used 4k but it keeps freezing up when I load samples from external. I also had to replace the usb drive and solder a couple things. Everything works fine now except it freezes. Any ideas?

check the memory first..chips and slots. make sure they're clean. put one memory module in at a time, test. You have to go thru a few trouble shooting step to see where the problem might be. I had a similar problem. It could be the main PCB board. hope this help