So U only have this problem with downloads? Or with a certain download? Can U open web pages ok, or watch videos,etc ? Does it do the same in safe mode with networking, or another user?
Try downloading your software from other website.
Try restoring IE settings to default (or whatever browser U have)
Try updating your browser
Try another browser
Try downloading to another location on your hard drive
Or try in IE safemode :
and press ok (then try to download)
Do U have enough space free?
Do U get any errors?
Check event viewer for related stuff.
Run CCleaner, and run a Malwarebytes, just in case. (google them)