You say you’ve not changed anything on your system but something must have changed for this to have suddenly started happening. If you’ve not installed any new software or hardware then the most likely cause is Martin has suggested a driver. It is sometimes the case that new drivers cause issues where the older ones did not. Remember also that these drivers are often installed automatically.
Aside from audio system drivers (check the dates on them to see if they may have changed recently) the most common culprits for sudden problems are graphics drivers. Try rolling back to an earlier version?