you almost certainly have a failing hard drive. it's failing to properly spin up and post sometimes and gives you the ?. Or it conks out while booted up and pinwheels you, forcing you to reboot. (and probably getting you a ? more often than not)
"genius" bar is not staffed by "geniuses" a lot of the time
get your hdd replaced before it forces the issue.
I work for the Department of Redundancy Department
