If your Download Manager is expired and asking you to put the serial number everytime you restart your PC.Well i have good news for you.
Download the Idm from https://kickass.to/internet-download-manager-idm-v6-19-build-8-with-crack-mumbai-tpb-t9050592.html
Follow the simple steps and get rid of serial number for good.
Download all the files
Install the IDM.
After installing copy the crack file(You will find it in the downloaded folder at the top) copy the IDM application file and paste to to the directory file in your pc where IDM is installed.In most cases you will find it in C: drive>Program Files>Internet Download Manager and paste it there.You will be asked to verify as a administrator.Clink Continue and its all done.