Turn on PC and...

[Janar]

Lol at the buzzer suggestion!

Don't really want to buy a new keyboard, 70(pounds) was a bit too much anyway.

Can't use PS2 thing because this has its own sound card (curious feature!) and has media controls, volume wheel, macros and lights as well as a USB port on the back, so USB is the only option

That's what I thought also, those functions etc. Media controls should work over PS2, but macros and lights not.
Then you just have to look around more in BIOS or just ignore the beep.

My other computer's keyboard also has "sound card", actually just helps getting sound from PC closer.

[9r2e5i3k]

My other computer's keyboard also has "sound card", actually just helps getting sound from PC closer.

You mean it actually has a sound chipset that works as a sound card or is it just a cable extension?

[b2311e]

Videos to demonstrate problem:

Beeping:
DSCF0090.AVI

BIOS/Startup/Device Manager (ignore the start Windows safely, it never usually does that)
DSCF0091.AVI

[Janar]

You mean it actually has a sound chipset that works as a sound card or is it just a cable extension?

Just cable extension, no sound card.