Lenovo G550 display

This machine has an Intel Express chipset, and was recently installed from scratch with Windows 7 Home Premium, the whole drive having been wiped by the previous owner.

All seems to run fine, with just a few minor audio hiccups as seem to be common on lowish-end modern laptops, and it plays videos with no problem.

When I try Windows Media center in normal mode (ie Restore Down from Maximize), the display is fine, but if I maximize the opening screen of Media Center, the top third of the screen judders but is readable, but the lower two thirds have multiple horizontal juddery lines as if the display can't handle the frame or line rate.

I don't know whether it has ever looked right, but there was a recent update to the video drivers from Microsoft Update. I've tried reverting back to the earlier drivers, but it's just the same. I've also tried going to the basic non-Aero display, but no difference.

What else should I try?

 

Further to the above and in the absence of any forum excitement about this problem, I've now discovered that if I go to the setup screen within Windows Media Center, if goes to full screen size, which locks fine, looks normal and can be read.
I have tried adjusting every parameter on the display, but as soon as I re-open this Media Center full screen, I have to bring the display back to less than full screen to be able to use it. It's only because the top third of the screen is more or less stable that I can do this.

If I go to the variable size screen and manually bring it out to take over the full screen, it also locks and displays fine.

When the fault is there, the top of the screen is normal but jitters a bit, the bottom 2 thirds isn't sync'd and is divided half way across, the left side being a greeney sort of olor, the right being dark purple.

Has anyone any idea what could be causing this?