it looks like a disc, have you a burning software newly installed or something similar.
a virtual disc mounted with some software, perhaps.
edit, also try this, eject your disc tray and if you have a disc in it remove it and close the tray.
see if the circle disappears, if it does insert the disc and see if it shows again
and click on the hidden icons to see if there is a similar icon there, if so click it or right click it to see what it is.
i had a google and the only thing i could find was this thread here,
unfortunately there isnt a solve, but its the same issue. Little circle on top left corner - MSFN Forum