Virtual memory error

My computer has Windows XP Home edition.It was ok till 7am
today.I don't know what has happened.Since then,it is
taking a whole lot of time to do even trivial tasks such as
switching between windows,clicking etc.When i press
Ctrl,Alt and delete,it is not even recognising that key
combination.When i re-start my computer,it will be ok for
the first 5 min,and later on it starts
freezing.Ocassionally it is giving an error message saying
that the computer has too low virtual memory.Sometimes,it
is giving a message saying that windows is increasing the
paging file size and thus during this process,it is not
taking requests any more.

Can anyone please help me,as i have to do a lot of
assignments today.
Thank You,
Radha.