Web Browser Discussion, Browser Talk - Slimjet Web Browser Online Forum

That box is under 'System' in Settings.

I found this on another forum, worth a try:
"Go to Settings and untick the box opposite: Use hardware acceleration when available. Restart the browser. Hope this helps."

If you are on windows 10, it's a known issue:
https://www.slimjet.com/en/forum/viewto ... f=6&t=1646

It seems to be an issue for windows 10 users:
https://www.slimjet.com/en/forum/viewto ... f=6&t=1646

Not much to go on, what happens when you try to play a video? What OS are you using, windows, linux? Did you try turning off any extensions? What else have you tried?

Could an extension be blocking youtube? Try turning them off. Does youtube work in another browser or just not in slimjet?

Sandboxie would give you extra protection also:
http://filehippo.com/download_sandboxie/

You might also want to check your pc at Shields Up. Click on 'Proceed' & run the various scans 'File Sharing', 'Common Ports', etc.:
https://www.grc.com/x/ne.dll?bh0bkyd2

Without further info, I'd just suggest you adjust the youtube video setting by clicking on the gear icon in the lower right. A lower setting might make it load & play.

Can you give us a specific video you say won't play?