Unable to boot into setup/safe/recovery mode....please help

Hi,

About to bin this imac I have (trying to fix this for someone at my work place) as I'm seriously wasting time....

Usual issue: Users do not know any of the passwords for the accounts on this machine.

Machine: iMac (circa 2010/2011)

OS: 10.5.8

Build: 9L31a

S/N: YM8300VLZE4

What I have tried:

Switching on, holding shift key (nothing happens - just loads to normal login screen)

Switching on, holding cmd+s (nothing happens - just loads to normal login screen)

Switching on, holding alt/option key (nothing happens - just loads to normal login screen

I have tried the above with holding the keys down when switched on, as soon as the chime starts, with releasing the keys when I see the apple logo, releasing the keys when I see apple logo then spinny thing.....

Same thing happesn - NOTHING.....Just goes straight to the usual login screen......

I don't have a CD on me and I'm mega frustrated