My Dell Monitor won't get out of Power saver mode and my Dell Dimensions 3000 has a solid yellow light?

My Computer has been full of problems today. I attempted to put in more RAM which led to me having a flashing amber light but it is now gone after I re-placed in the old ones in and now it has a solid amber light and my monitor won't start up. My monitor just says it's on power saver mode and to click any keys. When I do click the keys it does nothing (the keyboard is plugged in, along with the internet cable and everything else). Can someone help me regain access to my computer?