It could be an image 'burnt' on to the monitor.
If you have had one image on the computer screen for a long time it can cause it to burn onto the c=screen and it can cause a shodow effect.
Before you buy a new monitor i would surgest taht you try to borrow one before spending money.
+ if they shadows are moving it can be due to interferance (usually fuzzy lines) try moving the computer.
If the shadows stay in the same place most likely is screen burn