If it turns out that Flash Player isn't what is causing it, I would say it may be a lack of sufficient RAM.
If you have a lot of icons that open in the tray down by the clock on start-up, such as messengers or other unnecesary programs, go into each program and set them to not open when Windows starts. This would free up some RAM and should help.
If that's not it, the only thing you could do is upgrade your RAM. It isn't that hard to do, but depending on the type of RAM your machine takes, it may be a bit pricey.
Hope this helps.