NEW YORK - It will likely take several weeks to determine the exact cause of Saturday night's blackout in Manhattan, which left more than 70,000 customers in the dark at its peak.

Con Edison has centered its investigation on a transmission substation on 49th Street that feeds power to the six networks that were knocked out.

The blackout shut down several subway lines, and forced the cancellation of concerts and Broadway shows.

Con Ed president Tim Cawley says the company has ruled out foul play.

He also says old equipment and high energy use are not to blame for the outage.

"We sincerely regret the power disruption and the impact it had on the lives and businesses of this great city," Cawley said.

Cawley says the city's power grid is prepared to deal with high demand, which is expected this week as temperatures reach the 90s.

Senator Chuck Schumer is calling for a federal investigation into the power outage.

He says this type of massive blackout is entirely preventable with the right investments.

Following the blackout, Governor Andrew Cuomo says he is fed up with Con Edison and is calling for an indepenent invesigation into the matter.

Four subway stations lost power during the outage and Mount Sinai West was forced to rely on generators.

Speaking with NY1 Sunday afternoon, the governor said the blackout is not tolerable.

"This is not the first time with Con-Ed. We had the substation fire in Astoria we had Brooklyn substation fires, we went through superstorm Sandy where I don't think Con-Ed was adequately prepared. We've have had winter snow storms and ice storms where I don't think Con-Edison was adequately prepared. A situation like last night is just untenable. It can not happen. We can not have a blackout situation in a city like New York," Cuomo said.

The governor also commented on Mayor Bill de Blasio's absence Saturday.

Cuomo says different elected officials make wrong decisions about how they govern but that those choices are ultimately up to them.

After a night of cancellations, Broadway shows were back in full swing Sunday.

Some cast members from "Hadestown" entertained theatre lovers outside of the Walter Kerr Theatre Saturday night.

Many fans had their nights ended early because of the outages.

The Broadway League is urging people to contact their point-of-purchase for information about refunds and exchanges. 

The lights also went out at Madison Square Garden during a Jennifer Lopez concert.

She will be back on the stage Monday and MSG is telling concert goers to bring their original ticket, to gain admission to the Monday night show. 

Lopez addressed her fans on social media saying she was devastated about the abrupt end to Saturday's show and is looking forward to a big celebration on Monday.