I'm unsure if anyone else has noticed this but with the newer trainer UI it seems I have to push F1 a number of times before the trainer will say activated (sometimes it won't say activated so I have to tab out of the game to make sure) whereas with the older UI a single tap of F1 would activate the trainer.
It could be down to your PC specs, your CPU may not be powefull/heavily used or your GPU is being used heavily so when you press F1 it may have to wait a second until there is free resources for it to do so.
Computer data is like traffic, to get to a destination you have to go through many lanes,roads and motorways to get there and along the way you may get bogged down by heavy traffic. Same goes for data.
--------------------------------------------------------------------------- Great site for new games with constant deals