ALL files hidden, blank desktop, random music

My nephew downloaded a virus. I ran a scan and found 3 or 4. I went into the folder and deleted what i found, but all our files were hidden. I managed to unhide most of them, but when i click on program files from the start menu, it’s showing that all the folders are empty. The desktop is blank and when i try to right-click nothing pops up. Also, I found on the scan a virus in the system volume information folder named A0087220.exe. I tried to gain access to that folder but it’s always denied. Then I noticed that random music will start playing from the speakers and system restore won’t work either. SOMEONE PLEASE HELP ME!
AND when I try to google anything it automatically redirects me to another random site, like Target.com or Yellowbook.com