Volvo Repair: immobilizer or not, volvo vadis, vadis system

Question
My son has a great 2001 Volvo S-60 T-5 ,lately it takes spells not turning over.I'm lost,new key, key ring,and still runs for days then leaves you stranded once again
HELP................ Thanks, Donald  

Answer
Donald, unfortunately with these cars, I would have to do a bunch of tests as well as scan it with the Volvo VADIS system.  Everything is module or computer related. The only not computerized thing that it may possibly be is an intermittent fuel pump issue.  Roger