It's about PC security. And it's about things that an IT professional would never do, but that less IT-savvy people do time ...
PC won't boot? It's scary, but don't despair. There are a myriad of fixes out there. The only trick is knowing which one to ...
If you still want to use Disk Cleanup, start the tool by searching in the Start menu or by pressing Win+R, entering cleanmgr ...