Strange screen artefacts

[MikeinCairns]

I hope someone can advise. I have two identical systems. Lenovo laptop with DisplayLink USB to DVI.

The only difference is that on one laptop runs Win7 32 bit and the external screen is 1280x1024 and works perfectly,

while the other runs Win7 64 bit on a 1680x1050 screen and has horrible screen artefacts (attached) which look like pixilation and broken up picture.

Any suggestions about what to try.