Hey Lu, keep up your hopes
I have a final suggestion, it will take a lot of time, but sometimes windows is the cause. I suggest you reformat everything on your pc (backup the most important stuff first of course) and put a brand "new" version of windows on it. Upgrade it with all security patches and install the latest directX version too. Install all latest drivers of your hardware and install steam and RO again.
I know it's a lot of work, but if you really want to play this game: try it.
Your system will be fast again.
Make sure you know what you'r doing or ask a friend to help you with reinstalling. Don't forget to save your steamaccount data (loginname + password).
GL, Monk.