This is a major problem with Acer Aspire 5535 Laptops which Acer, PC World, Comet, Currys and Dixons are all ignoring. It's amazing that so many of these have been sold with this fault.
There is only one real solution, get XP on there ASAP - this solves the problem (you can keep vista on there too) and the laptop runs smoothly and VERY fast with XP too.
I done this and the 5535 is now (at last) working perfectly.
This may also apply to other Acer models too, like:
5530 5735 5720 5050
Hope that helps.
A full VIDEO showing how to do this is here:
youtube.com/watch?v=rdfU9TXIAd4