XP Pro, iPlayer Live & Flash & Hardware acceleration

[#1]

I went to stream a bit of BBC1 live yesterday evening, to discover I had sound but no picture using either Firefox or IE.  Catchup worked fine no problem. It had all worked not so long ago, probably had 2 or 3 Flash updates since I last used Live on this machine. (Still didn't work this morning,  ITV player Live is fine).
Couldn't discover anything obvious, my immediate thought went to Flash Player. I had version 11_6_602_168 and saw there was an update to _171 which I duly did, and made absolutely no difference.
I did a bit of Googling which revealed nothing recent and what was there was old & virtually all related to the Desktop version.
This morning I tried my other XP (Home) Machine which also had Flash version 168 and it worked fine. Head scratch.
Went Googling again which didn't seem to reveal anything more than before, although I decided to look at one not that recent live chat thread.
Well when I got to the end where they had tried just about everything else, Hardware acceleration was mentioned.
Low and behold I've had to reduce Hardware acceleration down to Disable all DirectDraw and Direct3D Acceleration, as well as all cursor and advanced drawing accelerations. 
At the moment I'm suspecting yet another Adobe foul up, but I could be wrong.
The only difference between now and when it last worked OK is Windows Updates and AVG updates (that I'm aware of). Going to go off to disable Firewall and AVG but not expecting it to make any difference.
Any thoughts as to other causes?

[#2]

That sounds like you disabled graphics hardware acceleration in Windows globally - what about disabling hardware acceleration just in flash player settings? (right click on a bit of flash content)

[#3]

I think the BBC was having problems yesterday, as there were perhaps three or four video clips I tried to watch from the BBC news pages that ran for tens of seconds then went into buffering, followed by error messages and error codes, then something like - "The content doesn't seem to be working, please try again later..."
I didn't have similar issues on any other site, and I was running Firefox 11 on an old version of Ubuntu.

[#4]

Thanks for the replies so far guys, as expected disabling AVG and Firewall made naff all difference. Also did a Hard Reboot just to be sure.
@ejs
Thanks, yes I had done what you said, but stupidly couldn't get to the Flash setting in iPlayer when on the failed live, so just now went to another bit of Flash - BTw speedtester  - and did it there. Can also get to it on iPlayer Catchup stuff as I've now checked. Main Hardware setting back to normal.
But I shouldn't have to do this, why did it work before, why the difference between two machines as well! 
@purleigh
Well I've still got these gremlins unfortunatly, whether it's related remains to be seen. I'd have expected to find more on t'net if it was Beeb related 

[#5]

It could be (probably is) a driver related problem. Slightly different as I'm Linux based, but if I use a generic video driver then I get fast play and no sound, whereas the proprietary driver works fine  That only becomes a problem when the manufacturer of the graphics card stops supporting my (oldish) hardware

[#6]

Well, driver problems are always to be suspected when things don't work properly, but when they were working fine and no drivers have been changed, it's a different ball-park I feel.
After a bit more digging, I fancy MS update KB2780091 affecting quartz.dll has something to do with this