Your card certainly should be ok, if only recently fitted though I would suggest refitting it to make absolutely sure of a good fit, graphics cards, as you probably are aware, can be very fussy about how they are seated.
It is always sunny in Southsea. Temperature in my pent-house suite is 24C.
Given that you have the opportunity to exchange it, it sounds like the best idea. I personally use a 12ms response time screen, but that is for gaming.
Still, given your problem is with DVD not gaming I’m quite surprised the 25ms response time is significant enough to be a problem. There’s a review of a Samsung with a 25ms time in last months PC stats. True, it is a very different model but I would have expected the below to generalize.
“Users who spend a lot of time gaming, and are hyper-sensitive how things look at 400FPS, will undoubtedly be best served by sticking with a CRT monitor. For those of you who aren't as anal about an LCD display with 25ms pixel refresh times, I think you'll find the 173P's other screen qualities lend themselves to a nice vibrant picture. Office work is a given, and I think Samsung 173P will keep any user more than happy for quite some time as they fiddle around on their PC, or even sit back and watch a DVD.”