For every week you have submitted a cert, you'll receive one credit. So if you've submitted certs for 52 weeks of a tax year, you get 52 credits.
In order to qualify for Invalidity Pension, you must have a total of 260 Paid Contributions (class A, E or H) and 48 paid or credited contributions in the last complete tax year before you make your claim.
If you didn't have 260 paid contributions when you last applied, and haven't worked since that time, you still won't have 260 paid contributions.
If you did have 260 paid contributions but didn't have the 48 paid or credited, then you may be eligible, subject to satisfying the medical conditions (incapable of work for at least 12 mths or over 60 & have a serious illness or incapacity).