Download decrease speed till 0kbs

[system]

I just recently reinstalled Windows 7. I downloaded avast and installed it, once I did that every file I tried to download, regardless of the file, it began downloading then the speed decreased within a few seconds to 0kbs.

For awhile I didn’t know what it was but when I uninstalled Avast the downloads returned to normal.

Is there anything that can be done or will I just have to stop using Avast?

[system]

Also, during the time I was unable to download I was still able to surf and use Spotify with no issues though sometimes the connection completely cut even though Windows said I was fully connected to the internet.