Mainline rail passengers and Olympic visitors face major disruption all day on services to and from Euston.
For many commuters it was a repeat of problems they suffered getting home last night.
Virgin Trains and London Midland services are subject to cancellation, delays and amended timetables.
Fans heading to the Canada versus France womens' football bronze medal match at Coventry - starting at 1 pm - are strongly advised to allow extra journey time and check before they travel.
There were delays of up to 45 minutes with fast trains making additional stops.
Disruption follows problems with the overhead power cables near Milton Keynes.
More than 100 metres of cable crashed down around 6pm last night disrupting thousands of passengers heading home.
It caused huge damage to other power and signal cable infrastructure as it came down. Cable theft is not suspected.
Network Rail (NR) engineers worked through the night to restore service but the damage is so severe only three of the four lines at Milton Keynes are open - a situation which will last all day. Repairs will continue after close of service tonight.
An NR spokeswoman said: "There is a lot of damage. We managed to get two lines open by 8pm last night and work continued through the night.
"We now have three out of the four lines open.
"An amended timetable for services to and from Euston will run all day.
"We apologise to passengers for the disruption last night and this morning. We also advise fans heading to the Coventry match to allow extra time.
"Our engineers aim to complete repairs tonight will full service resuming tomorrow morning."
On the Tube, Piccadilly line passengers suffered severe delays due to a signal failure at Action Town.
This also caused delays to District line services.
London Overground services to and from Euston - including those to Wembley - are not affected.
A normal service later resumed on the Piccadilly and District lines.
