Shall I try the card with a trusted friend maybe, as this friend, is not so much a friend, just someone I say ok to
Hmm, never one to cast aspersions but in this instance I will say that it is most unlikely that the 290x worked in a HP Pavilion 550 Gaming PC, you will have to draw your own conclusions from that I`m afraid.
A good friend who has an adequately powered system or a local tech or tech store, the latter may charge a small fee so best to ask them first.
Maybe I would be better of selling it, and buying another 280,
Wasn`t aware that you had previously had an R9 280 only the R9 290 you mentioned in your OP.