Major problems produce major stress. Yet the more stressed you feel, the more difficult it is to problem-solve. Try the following.
Examine current commitments and mark those that can be shelved or delegated.
Assess how much time you can allocate to this new problem. Review your diary and schedule action time into vacant slots.
Dissect the problem, its aspects and knock-on effects. Cross out those you have no control over, prioritise the rest.
Create a step-by-step strategy for each aspect. Enter action points in the diary slots you've already allocated.
Share your plan with a positive-thinking colleague or friend, and set a date for celebrating Solution Day.