First check if they are in the Recycle Bin. If so, restore them.
If you can get to the command prompt, run sfc /scannow.
If you have a backup, use that.
If you made a recovery drive (recommended!), use that.
If your PC came with recovery discs or you made them, use those.
If none of the above, download a Windows install disc or stick from Microsoft, and boot from it to initiate repair options.
I have accidentally deleted multiple important files from my laptops c drive, now none of the icons on the tool bar will work except a select few. The Windows icon won't start even on the keyboard so I can't get to the computer settings. What can I do to get the important files back onto the c drive?