DST long test - not progressing? i15 5520 laptop

2-3 year old i15 5520 running Win 8. When working on laptop, the fan will speed up at times, which slows processing. Laptop is not running as efficiently as it did. Ran a pre-boot diagnostic test last night. It completes first part - no problems detected. 2nd part it seems to be running fine and then at what seems to be 95% complete, it doesn't seem to be progressing. Escaped from test and tried again. Same result. At 96% complete for 20+ minutes no change. No error codes, no results logged.

Do I need to allow the testing to run longer or is this representative of a problem with the hard drive?

Thank you!