Flymo Roller Compact 4000 won't start?

Hello,

I have the Flymo Roller Compact 4000 (RC4000) lawnmower, which has worked perfectly for the last three years.

Last week, I managed to break the power cable and have purchase a genuine Flymo replacement. After less than five minutes of cutting, the lawnmower simply stopped and refused to start back again.

I have replaced the fuse and tried another Flymo cable, but the lawnmower will not power up. It doesn't make any noise or anything when I try, just as though I haven't plugged it in properly.

Rightly or wrongly, I dismantled the small black box on the handle, where the start button is, and all of the connections were secure. I have also cleaned the grass box sensor, because I realise it wouldn't start if it thought that the grass box wasn't in properly.

Any ideas, please?