When I try to resume a download, IDM fails to do this although it shows "Yes" as resume capability. What is the problem?
When I start a download, speed is good but then it drops to zero and download never completes. What is the problem?
Such problems may occur because of conflicts between IDM and other applications. It can be some FireWall/Antivirus/Internet security application which controls traffic and all files (file parts) that are written on disk and can change or cache them.
For example such problems are confirmed with Bit Defender 2012:
Also there are confirmed problems with Sonicwall:
In the latest verison of Bit Defender this problem is solved. Right click on the BitDefender icon and select "Update Now". Wait for the process to complete then restart the PC.
Also some FireWalls and Antiviruses may be not ready for Windows Vista, Windows 7, Windows 8/8.1 or Windows 10 and work incorrectly.
Please try to TEMPORARY completelly uninstall your FireWall/Antivirus/Internet security application. Just disabling it is not enough because some of such applications keep blocking access even if you you switch them off. Then look if your problem persists. If it is solved, then problem is definetely caused by that application. Please read this web page. Maybe your security application is present in the list on the page and you can read how to configure it to work with IDM. If it does not help, you can try to contact its developers and ask them for solution or try some other FireWall/Antivirus/Internet security.
If it does not help, maybe you have some application that functions like FireWall/Antivirus/Internet security and you do not even know about it. It may have something like "Protector", "Defender", "Spyware Remover" or "Cleaner" in its name. If you find such application on your computer, try to uninstall it as well and look if your problem persists.
The same problem may happen if you use some proxy in "Options→Proxy / Socks" IDM dialog. Try to disable it or at least use another proxy. Also maybe your provider uses some external proxy.