windows did not start successfuly

turned on my system this morning and received this message:

a recent hardware or software change may have caused this. (I did not install anything recently, not sure about what software that may have caused this issue)

message also states: if your computer stopped responding, restarted unexpectedly or was
automatically shut down to protect your files and folders. choose last known configuration to revert to the most recent settings that worked. if a previous startup attempt was interrupted due to a power failure or because the power or reset button was pressed. or if you aren't sure what caused the problem choose start windows normally.

it then gives choices safe mode safe mode with networking and with command prompt
below that is shows start windows normally
and below that it shows use the up and down arrow keys etc to highlight choices and then shows seconds until windows starts: 0

system would not allow me to do anything. was not able to use keyboard or mouse.

I have never seen this before so not sure what has happened.

but I manually (pressed the power button) to shut down gave it about 10 mins. restarted system. got same message but the shows seconds until windows starts:
had a countdown of numbers and was able to press the enter and computer started up normally.
not sure at this point now what or where to go to see why this is happening.,
fearing the worst that my system is doing a precursor to crashing???
am about to do my qrtly backup. just in case.
this happened on my windows xp sp 3 Compaq desktop not sure what else might need to help.

I am not using that system at the moment to post.
any suggestions advice would be appreciated.
thanks