Did you have a power outage to you whole house?
Or did the job you were trying to do just shut your computer down and prevent you from checking that the job had been completed?
First see if your old AV program has an uninstall option in it's start menu folder. While you are at it un-install Limewire if you still have it installed.
If the AV program doesn't have an uninstall option in your start menu look in your Program Files directory and see if your old Antivirus software still has it's installation folder in there. If there are any signs of your old AV program manually delete it from there and AVG should work fine as your new antivirus system. Same thing if there is any bits of Limewire left in your Program Files directory delete them too.
As far as your main problem is concerned I'm at a bit of a loss to explain what could be going on. Have you tried booting into safe mode and then try to uninstall your java installation while it is in safe mode? (usually this is achieved by holding down the F8 button while your computer is booting up). if you manage to uninstall your old java RTE go to the java download site and download the offline RTE installer and see how you go at installing it. The webpage you need is: http://javadl.sun.com/webapps/downlo...BundleId=20287 that should give you a version that can be manually installed by you. While you are in your Program Files directory clean-up (delete) any left over bits of your previous Limewire install as well (if there is anything left of it) If you have success re-installing your new RTE then try to install the latest version of Limewire from here: Lime Wire » Download LimeWire going for the free version first of course. Let us know how you go at these first instructions and then maybe things will be looking up a bit.
Another thing worth considering is reading as many of the "Sticky" posts at the beginnings of each of these forums in the hope that there may be some mention of another way to deal with your dilemna.
Just out of interest what brand was your old antivirus software?
This has got me a bit baffled and to be honest and I'm hoping that one of the moderators jump in at some stage with some other suggestions for you to try.
But that's all in the future, for now you've got enough to keep you going until next time we exchange posts probably tommorrow.
Good Luck!