Q: Car doesn't move at all when iI engage the gear in both drive and reverse, rather shows W on the dashboard for gear position 2001 Volvo S80

Hi there - the "W" displayed on the instrument cluster means that "Winter mode" is selected. This means that 2nd or even 3rd gear starts are invoked (rather than 1st) in order to get away from a dead stop in snow or icy conditions. This does mean you accelerate slowly, but should not mean you can’t move at all. if checking with your mechanic who did the transmission flush doesn’t resolve the problem, I recommend a transmission inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.