Strange FS9+PC freeze on APP into EGLL - Now what?!

In the past 2-3 days, I cannot approach EGLL from any direction in FS9 without suffering an explicable freeze of FS9 within a 1 to 9nm radius of any of EGLL's destination runways. It's happened 5-6 times now, using the POSKY B742 with Massimo's panel. It also happened using the default B744, but not using the default Cessna.I have recently adjusted my DISPLAY settings downwards to give me more fps for flying and fps look great on initial approach into EGLL 27R and L (for e.g.), but at some point after that, the sim freezes or near-freezes (goes into ultra slow motion over a period of 3 to 5 minutes, 1 frame per 30 seconds, sort of thing).I tested the exact same aircraft into KIAD 19L and all worked perfectly. So I think I have a scenery problem.I also think it could be a scenery issue because visually, the textures around EGLL all load visibly when overflying the airport and flying the approach. There is the slight appearance of texture stutters even with fps at 21 fps around EGLL. I have the fps counter on and it usually indicates a sudden drop in fps from 18-20 fps to about 7 to 9 fps when the freeze occurs. I cannot ctrl/alt/delete to get out of this. I cannot bring up the Windows Task Manager either.The freeze appears to be total at first but after 3 minutes or so, the view shifts and random FS views of my situation appear on the screen. The best way to deal with this freeze or near-freeze is to switch off electrical power to the PC and re-boot. It takes ages to do this and recycle everything as I also use FSAutostart.I have Ultimate Traffic installed and it's always worked flawlessly since installation. I wondered if I have any duplicate bgl but I don't think that is the case. This has never happened to me before.I don't think I have heat issues and my PC has performed generally very well with FS9 for a long time. I don't think I've ever had such a strange freeze situation. I've never had trouble approaching EGLL in FS9 before. It's a total mystery to me (but of course, it's MSFS!)Can anybody think what is causing this?Thanks!JS