Sounds to me like your laptop is either getting a little long in the tooth, or did not ship with enough ram for the operating system chosen to begin with. The fact that you mention this happens at startup points to this. As your system ages, windows updates, programs update, you install new programs, etc., all of which take a larger and larger chunk out of your systems resources, making it necessary to upgrade or replace your system.
You might try to revert your laptop to factory settings, which would remove any unneccessary clutter that is eating into your ram. Make sure you back up all your personal files prior to reverting your laptop to factory settings. You will also have to reinstall any programs, etc. that did not originally come with the computer. Here is a link that would assist with this.
http://www.ehow.com/video_4766635_reboot-computer-back-factory-settings.html
you might also try to upgrade your system with more ram. this isn't an easy process with a laptop and it isn't always possible depending on the specific laptop you have, so it's best for you to check with the original manufacturer either online or via tech support (if you still have this available) to make sure you 1) can upgrade the ram, and 2) get compatible ram for your laptop. Here is a link that will assist with that as well.
http://www.youtube.com/watch?v=yirNejnzbEM
If your system is particularly outdated, it could just be that it is time for you to replace it with something a little more powerful. This is an option you would want to consider as well.
Hope this helps!
Kel