Depending on what important info you have on the machine, there should be a way of restoring to factory settings, via a hidden partition, or discs that you should have made when the netbook was first used. Have a look at the documents that came with the machine. Note that you will lose ALL your docs, photos etc as the netbook will be restored to 'as new'.
If you have information you don't want to lose then try tapping F8 ( or F5) on bootup to see if you can get to safe mode. If you can then try a system restore.