Besides which qualifications to study, the main question surely should be can you "afford" to change careers at this stage of the game. Depends on were you live etc etc but helpdesk wages are very low and generally only good for those skipping out of school/college with no commitments etc. If you have wife/family/car/house any or all then you will need to look at the average salary for helpdesk and desktop support to see if you can survive the 2-3 years on average it takes to rattle through those positions.
Helpdesk positions generally do not require any certifications, only a certain mindset so dont go thinking that you need a certification before you start looking for helpdesk work if its feasible.
Biting the hand that feeds IT
