|Since it last worked properly, have you...|
- dropped the laptop or subjected to a physical jolt ?
- spilled liquid on it ?
A common thing that can happen with ram, even ram that worked fine previously, is the ram has, or has developed, a poor connection in it's slot(s).
See response 2 in this - try cleaning the contacts on the ram modules, and making sure the modules are properly seated:
For a laptop, or netbook, you must remove both its main battery and AC adapter before you do that.
For a brand name computer, see the Owner's or User's manual if you need to - how to remove or replace the ram is usually in that - it may already be in your installed programs. If you can't get into Windows, it may be on a disk that came with the computer, or you can go online and look at it or download it - it's in the downloads for your specific model.
I'm assuming you HAVE NOT changed which ram you have installed in the laptop since it last worked properly.
I you HAVE changed the ram, the ram you installed may NOT be compatible with your laptop.
If you still have the ram that was in it before, trying installing that to see if your laptop then works fine.