The phone will not work at all now and only shows an icon depicting the phone and a pc connected with an exclamation in the middle. I have taken out the battery etc but to no avail. The PC now doesn't recognise the USB connection.
What do I do now?
From the comments it sounds like you've gotten back to Download Mode, so that's good. If not, try different button combinations in conjunction with battery removes and being plugged/unplugged into USB. Something should get you there.
Once you're in Download Mode you're probably going to need Odin to fix your device. You can use my instructions here for Odin.
I found this link to be useful. http://forum.xda-developers.com/showthread.php?t=775911
Essentially, you have to remove the battery, SIM card and the microSD card. Then wait for a while and put everything back and connect the phone to the pc running KIES recovery. It worked for me, although its not clear to me what really clicked it.
the problem is that you have bricked your phone. fortunately for you, its just a soft brick and not hard brick. phones can be repaired from soft brick.
run "emergency firmware recovery" option in kies. it will work. run revcovery using the same pc. if you cannot run from same pc, get the recovery code from that pc and use the that code to run recovery from any other pc
from what you have said, i can advise you that you should not attempt to use odin right away to repair you phone. if you still insist on using odin, i suggest you google about itthoughly before flashing using odin.
this problem can be rectified using kies and i suggest you do the same. emergency firmware recovery option is given in kies for your problem and such.
From what you have written it appears that your phone has been "BRICKED." The computer that you were using to perform your KIES update via the USB connection was not capable of handling the update and unfortunately your phone has become inoperable.