Original post : Fix slow boot - Guide for Windows XP, Vista, 7, 8, 10.
For more information on how to check HDD/SSD for failures, read this this guide.
For more information how to delete temporary files, read this guide.
chkdsk C: /r
sfc /scannow /offbootdir=c:\ /offwindir=c:\windows
chkdsk C: /f /x /r
Reinstalling Windows means you will loose all data if you don't backup your personal files.