Trouble with Solver
 

I am unable to add Solver. I have Office XP Professional and when I check
the Solver add-in button, Solver doesnt show up under tools. The strange
thing is that it shows up sometimes and then I use it and after I quit Excel
and re-open it, though Solver is checked as an add-in, it isnt available
under tools. I then unclick all the add-ins and then check them again and
sometimes Solver shows up under tolls and at other times, it doesnt. I am
unable to retain Solver as an add-in.

Can someone help me Please

Many Thanks