Unable to log on - message states "please wait..." been like that for hours - tried switching off and on

As going through safe mode should help.but if that does not helps.its quite necessary that mother board of the computer is faulty.
but before getting the mother board repaired.try this instructions.
unplug all the wires at the back of the cpu the (tower),then open the cpu cover by removing the four or six screws.then inside you will see the power supply ,the hard disk,the dvd or cd rom/drive ,mother board.do just 1 thing.first mark all the wires with a marker and take a note where they are all connected.then remove all the wires of this device from the mother board,remove the sound card,the ram (memory ) and CMOS battery,fitted on the mother board care fully.then take a air blower and blow the air on the mother board for couple of minutes.make everything internally dustfree.then slowly --- slowly connect every thing properly and tightly as it was before.it will mostly work.but if still the same problem,then its quite sure that the mother board is faulty and it needs reparing.
but yes its worth reparing because there is power in the cpu and it comes up till the ---- please wait --- screen.so the cost of reparing will be negligibe as the board is not completely dead.
this will help.
please do rate the solution.thank you for using fixya.keep updated.thanks.

Turn the computer off, a little before the windows logo comes, start tapping on f8 to get advanced start up option. Select Safe mode. Try to login in safe mode. if you can then turn off the computer and start it normally.

let me know the results.