Margaret,
Your description is a bit hard to understand – but let me try.
Typically, the sort of echo you appear to be describing takes place when a speaker produces a sound, that is then picked up by a MICROPHONE, which sends the sound back to the SAME speaker with a small delay.
I suspect that you have a microphone on your computer somewhere – they’re building them into a lot of systems to enable chat, and phone over internet etc. – and the control panel has enabled something that has turned that microphone on – and that you’re getting an echo loop from the speaker to mic.
When a system is working properly, the speakers are muted when the mic is turned on. And the mic is disabled when the speakers are in operation.
But with so many products and pathways in a modern computer or sound system, it’s perfectly reasonable for a system go get in a mode where they’re BOTH on – and the echo takes place.
Look in your SOUND settings for a way to turn the microphone off. Or if it’s some kind of external microphone, look for a way to shut it physically off – and that should take care of the problem.