The card says you cannot play assets of events. The rulebook states that playing a card is to pay its resource cost and put the card into play, usually using a play action.

Thus, cards already in play are unaffected. You can also commit cards from hand to skill checks.

To me, this card brings up an interesting question: is an encounter card balanced if it punishes certain playstyles disproportionately? For example, is The Tower • XVI unbalanced because of how severely it punishes skill-reliant investigators like Silas Marsh and Minh Thi Phan? Or, in the case of Dissonant Voices, is it unbalanced if it shuts down investigators that are reliant on playing events, like Nathaniel Cho?

Of course, as others have said, Dissonant Voices isn't a complete shut down; Nathaniel Cho can still punch monsters or Sefina Rousseau can draw cards, for example. However, the gap between those investigators' effectiveness when Dissonant Voices isn't afflicting them and when it is concerns me, similar to how some investigators (like Charlie Kane) become mere shadows of themselves during The City of Archives. Not being allowed to play what you intended to play with little room for countering strikes me as potentially poor game design; the "Yes, but..." design of most of the game's counters to player strategy (i.e.; Final Rhapsody: Yes, you can turn s into 0s, but those s are also time bombs when you draw your signature weakness) looks more interesting, and, to be blunt, more fun, than flat denial like Dissonant Voices.

TL:DR; This new user drew back to back Dissonant Voices with Nathaniel Cho and got salty about it.