Removable media rejected straight away

As im pretty new to macs i dont know if its just be being an idiot or a genuine problem but i have asked all my friends that have macs and they don't know either.

Basically what is happening is that when ever i insert either a pen drive or my iPod nano (3rd gen) it will just eject it straight away without warning or asking me if i want to do so.

but if i put the devices in before i turn my mac on, then switch on it recognises them and doesnt eject them, but it is really annoying having to turn my mac off and on again when ever i want to connect my ipod

i tried ringing the apple store but they said as my mini was out of warranty that i'd have to pay for their help but they suggested i go on apple.com/support and see if i could find and solve the problem myself

this didnt help

I've tried what it said on the apple site and also tried repairing disk permissions

none of this helped

please help

thanks in advance

Have you enabled disk use on that nano from iTunes. Try it next time you get the nano mounted, otherwise itunes will kick in and eject your ipod

yeah disk use is enabled, but its not just my ipod

i hope i don't have to re-install OS-X

Is this plugging into a usb port by chance? Have you tried using a different port?

yeah i have tried all 4 usb ports and each time it just ejects it, the power is still there cause my ipod charges and the red light on my pen drive still lights up.