Read about known function for dsolve/numeric
I used method lsode. As this problem is stiff, use stiff = true, but you have to provide the diff of the function (see the help above above).
I ran for shorttimes, it is taking long. You can read about lsode options if you want to use this. Also, please consider using classic worksheet or maple format for display. Most of the time was spent on copying and pasting from your code to mine, not the actual solution itself. Try classic worksheet, and see for yourself how easy it is to copy paste commands or write a code with large number of sentences/commands.