Screen replacement

Assuming it's out of warranty or was damaged by the user, contact a local repair shop for an estimate.  Or, contact Dell for a repair estimate.

https://www.dell.com/support/kbdoc/en-us/000223825/out-of-warranty-support-options

If the unit is older, comparing repair cost versus replacement value is smart too.

My friend runs a service business and he does the same with equipment repairs, sometimes a quick diagnostic tells you whether fixing it makes sense or if the money is better spent on a newer machine.

Replacing the LCD-Panel on an inexpensive All-In-One desktop is not usually financially viable. Not just the parts, but labor would be high. Seems like even a working refurbished computer would be better (and keep the old one for parts).  

That's the draw-back of buying an All-In-One machine.