Customers had been greeted with an apology page when they tried to order
Sainsbury's has fixed a "technical glitch" which put its online ordering system out of operation for two days.
But supermarket customers left without groceries will have to wait until Saturday before deliveries resume.
Sainsbury's website is now back up and running and customers are able to amend existing orders or place new ones.
The company said about 20,000 people had been affected by the problem on Wednesday and Thursday and it has offered £10 vouchers as compensation.
In a statement, Sainsbury's said: "We experienced a technical glitch which affected our ability to process orders.
"We have been contacting customers whose orders have been affected over the last couple of days and would like to apologise once again for the inconvenience this has caused.
"We have spent just over 48 hours fixing the problem and the website has been thoroughly tested."
The supermarket giant said deliveries would resume from 0800 BST on Saturday.
A spokeswoman said no-one had hacked into the website and customers' details had remained secure during the shutdown.
The fault was spotted on Tuesday afternoon, and left customers facing an apology page when they tried to place an order.