Thin whites lines at top of t.v. screen - Insignia IS 20" TV040919 TV

These are retrace lines. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts.
http://electronicshelponline.blogspot.com/
Type in this key phrase " my service table today " in the search box at the top right of the display window of the home page, to get gathered some pages which has the details of practical experiences to the author of that site.

IMO Seriously for $119 it's not worth it.
However, it does sound like a capacitor problem
If you are "Serious" about fixing I'd find a TV repair Forum.
Else I'd go here and get a new one.
https://www.walmart.com/browse/electronics/32-inch-tvs/3944_1060825_2489948_7156390
Best Wishes.

If you wish to get some details; visit the site linked here. Pull up older posts.
http://electronicshelponline.blogspot.com/
Line faults & possible causes to LCD & Plasma screen are given with illustrations. You can get an idea about the fault to an extent. Faults to all LCD & Plasma screen are similar, irrespective of its brand and screen size.
Search the site by type in the "BRAND NAME" of your device; (Exclude the model number), in the "Search box at the top right of the display window of the Homepage" to get gathered related posts

T con board is responsible for the image you see on screen as well as any anomalies.

You got a bad LCD screen. no immediate resolution aside from getting the LCD replaced. if your system still has warranty call Dell for replacement.

Hope it helps!

check on bios if still there then monitor needs repair.

change the 33uf 35v at the vertical filter

Thans!

The picture tube is fine.
Those whites lines at the top of the screen are caused by a dry or leaky capacitor(s) nearby the vertical amplifier IC.
Let me know if you require further assistance.

Thin white dashes on top of screen is PERFECTLY NORMAL. It is nothing wrong with the TV, it is the broadcast. What you are seeing is the very bottom of the timecode running. It doesn't happen all of the time or all channels. It usually happens with old 4:3 commercials predating "Digital TV." This is mentioned in your Users Manual. You should be able to adjust the horizontal/vertical position in the menu settings.

The several thin white lines at the top of the screen is the warning that the vertical output IC is not getting the boost voltage it needs to run correctly. The IC cannot operate for long like that and shorts out inside, which is when the vertical collapses altogether and you get the thin white line through the center of the screen. The good news for your son is that he had nothing to do with that, and it has nothing to do with the cable F connector. The set needs to be serviced by an experienced tech who will restore the boost supply and replace the vertical output IC, and when I do that I charge $75 but techs in your area will vary, so be sure to ask around.