It's hard to know if there are any problems. Something is causing hard drive activity. It could be a routine scan being done like a scheduled defrag, anti-virus scan, etc. It could be malware that's taken over your machine. When the hard drive light is on you could open Task Manager and see what's using up your CPU. (Right-click an empty spot on the taskbar > start task manager. Or press Ctrl+Shift+Esc.) This could be an indicator of what's using the hard drive. You could also open Resource Monitor > Disk tab for a more detailed analysis.
Resource Monitor