Low signal strength and 2/5 Bars Wireless?

Could anyone tell me why im only getting 2/5 bars with my wireless router and only getting from 18-24Mbps when I have one the newest linksys cisco routers E2500 N holds 2.4Ghz+5.4Ghz has 150+Mbps also am running broadband comcast getting 6-10Mbps but getting actually 4Mbps down and 4Mbps Upload. I'm clueless guys help please! BTW my xbox is hardwired but getting Full 5/5 Bars and my wireless on my computer is only like 15 feet away from my router getting only 18-24Mbps an sometimes is says very good signal but most times it says "Low"... and flickers back sometimes.