You'll have to give us some more information...
The Acer Aspire one usually runs Linpus Linux, have you changed to another distribution or are you still running Linpus? I've got an Asus EEEPC so my comments will be a bit general I'm afraid.
I have messed something up and now I have kde and gnome at the same time
What exactly were you doing? Did it work OK till you rebooted? If you can't get past the login I don't understand the "KDE & Gnome at the same time" comment. You can usually select one or the other at Login.
Can I just confirm that it boots to the login screen but you can't move the pointer and you've no response from the keyboard?
I believe the Aspire one comes with a restore DVD? You'd need to buy, beg, borrow or steal (no, I don't really mean the last one!) a USB DVD drive and try to boot from that.
Can you break into the BIOS to select the boot device, Usually <del> or <F1> or something which flashes up on the screen for a second or so during boot (This would mean that the keyboard works
) Anyway, that's enough to be going on with for now
Oh! and Welcome to the LQ and the forums!