The fuse box as iancseries2 said is just clipped in. You will see 4 clips, and all you need to do is just pull the sides of the fuse box gently and use the wiring grommet to just ease the fuse box past the clips then you can gently lift it up. However if your car hasnt been played about with much u won't be able to lift it very high, the wiring is cable-tied in place under the dash, when cut it gives you a fair bit of slack, you'll have a right nightmare if the cable tie is still on.

Check the relays towards the back of the fuse box they are common to burning out. If however you do need a new fusebox you will probably be better off buying a new loom, as the fuse box isn't easily seperated from the wiring.

Something they changed on the mk5's, everything just plugs up (just aswell though mk5 fuse boxes are absolutely crap!!!!)

Sounds to me though to be honest like the main positive busbar is breaking down.