There are a lot of possible causes.
- How old is the monitor? NEC has a fairly good reputation, but all monitors will eventually die as components age, especially the picture tube.
- Is this a new problem. Was it sudden or was it barely noticeable?
- There are some user maintenance actions you can try such as moving things away from the monitor (magnetic speakers, cables, other monitor(s), etc.). You can also degauss the picture tube. Most monitors have this function built in, and can be accessed through the monitor's setup/maintenance menu (on the monitor, not the PC).
BTW - I have used an NEC monitor almost continuosly since 1982. If it wasn't so small, I'd be using it now.
Dell
