The ps store is on mantnance when it will be ok to go ok
The PS Store is in the process of being updated with new content.
if that's not your issue & you've been experiencing this for some time, please delete the PS Store Application & re-download/re-install it, also check that the date & time on your PS3 is correct.
Customer Service - 1-800-345-SONY (7669)
Account & billing Support -1-877-971-SONY (7669)
Available Mon to Fri 8am - 8pm PST