research research and research!
find out who exactly uses your site....
it appears that maybe school people and business people use your site.
playing games while at school, and playing games while at work

sunday is a day of rest for these people and your going to find it very hard to get them to go to this site on their days off, because they will be at home with their 'home' computers.... with games installed on the hd which you might not be able to compete with.

either try to target the website at other users (not sure how to do this, maybe MAC games, i dont know if MAC's still suck for games, or online rpg's etc. muds etc.)

or try and create a community, which is your best bet at dragging these people out of their homes and onto your website. Forums, chats, high scores, with personalised competition, like for example, get a quick user access so you have to have an avatar of your face or something... get some high scores going with trophies on the main site.. people might even compete at this **** just to piss off another user, and try and do better than them. A little bit of rivalry/competition/pain never hurt anyone

just my thoughts