Tracks turning into Stop Motion animations half way through

[Jdeadevil]

I'm getting sick of this, I'm using Virgin Media at 20mb/s, I thought using this computer for FFR (as oppose to the one me and my dad use, B.T. which is usually a maximum of 5mb/s) would fix the problem as it's fast, but I was wrong. I can't even play the game on it's highest quality setting without it being glitchy as hell. So sure enough I use the lower setting, but then it starts turning into a crap GIF animation as it jumps down the screen. What the hell is the problem here? Normally it takes about two or three attempts of "Booing" out and it just about works, before I get bored of the song and have to do the same process on the next song. The worst for this is "Reversing Darts" at Lvl 9.

Can anyone help me out here? It's winding me up.

Edit: It's worth mentioning, this is my mum's computer, I haven't just got Virgin Media just for the sake of hoping FFR would be smoother. ^_^'

... Okay I'm just going to avoid the temptation to play for the night, seen as EVERY SONG is practically glitched and messed up.