Hi Malin! Your computer question got sorted into the "Mac"category...is that indeed the case, that you're using a Mac?
Also, can you tell me any other information about this problem? For instance, do you know (approximately) how long ago it started? How long do the symptoms last once they begin? How often does this happen?
To rule out (or confirm) the presence of a virus, let's have you download and run a free virus scan: TrendMicro
Please let me know what the scan finds!