Well, after doing a little research, it would appear that the problem you are experiencing, other owners of an Acer 5520 have also encountered.
If it is the same, and it seems to match your description of what is occurring, then It could be a problem with the nVidia graphics GPU chip, assuming your system has the same hardware as described in Blogs and Youtube videos given below.
Take a look at:
http://www.wimsbios.com/forum/topic11831.html
then watch the youtube video that shows your symptom
www.youtube.com/watch?v=a5rgc1phdrY
followed by watching the Youtube 'How to Fix' videos, but you may want to seek some additional help to carry this out as it involves the use of a heat gun. (Hair dryer might be a substitute if you feel competent, but you would need to be careful.)
www.youtube.com/watch?v=cBy7rOiQw18
and also,
www.youtube.com/watch?v=XykI-u9mSOY
Hope that sort of assists!