6n 1.6 glx extreme power loss (possibly electrical)

[MattPo-Low]

hi all first post and i need some advice lol

i have a 1996 polo 6n 1.6 glx which has recently lost all power. The car will run fine on start up for roughly 30 seconds to a minute and then loses all power, still revs all the way but very very slowly and its really struggling, the strange thing is if i reset the ignition(key off then back on) whilst in motion the problem rectifies itself for roughly another 30 seconds then returns to running badly, the same goes for if i stop an turn the car off and then restart it. I've had a friend hook it up to a computer which gave a coil pack error i have changed the coil and the problem remains. I have also changed the fuel filter and checked the various fuel/ vacuum hoses although i cant see it being a mechanical error due to the fact that if i reset the ignition its fine for a small time.

Any suggestions appreciated

Cheers
Matt