inno3D Tornado geforce 4 MX blank screen

Hi.

My old graphics card (ancient matrox card)
died on me a few days ago. Desperately needing
my machine working (and no onboard graphics)
I bought a very old ISA graphics card for £2.00
from a local charity shop and an inno3D Tornado
geforce 4 mx from the one and only local computer
shop that sells parts (rather than complete systems).

The ISA card is now helping me post this!

Anyway, onward to my problem! My PC boots OK.
The memory test comes up clearly as usual,
however after this, my screen goes blank with
a flashing cursor (underscore) in the bottom left.

Everything is 'working' as I can do things normally,
just with a blank screen. I logged on and rebooted
the machine manually (so all the other parts are
working - there is just nothing going to the screen).

When entering the bios, the screen is completely blue
with a red square 'blob' that changes shape (depending
on the length of characters in the menu option). I can't
actually read the options, but the moving red 'blob'
shows that everything else is working.

Any ideas on what is causing this?