This could get very messy quickly, so perhaps call 'that mate' over who works in IT.
It's likely the BIOS upgrade has messed up or lost your BIOS settings. BIOS stands for Basic Input Output System, and as it sounds, it's at the very very base of how your PC communicates with it's components - the hard drives off which it reads and boots into windows being one of those components.
What's probably happened is that it has forgotten or carried over incorrect details about your hard disks so either doesn't know they are there or thinks they are somehow configured differently.
When you boot the computer there's probably something on the screen like 'Press F2 to enter setup' etc - the keys vary.
If you get this, and you enter the BIOS setup, there is probably a setting on detecting / configuring your hard disks - again, this varies depending on the manufacturer of the BIOS.
*IF* you get that, and it automatically finds your hard disks, and sets up the appropriate drive geometry automatically, then you *MAY* be able to 'Save settings and restart' or similar.
*MASSIVE CAVEAT*
If you had setup any form of none standard drive geometry or odd configurations, detecting and using the wrong settings will basically make your disks read back garbage, and should you write any information to those disks, there's probably no going back.