Computer won't go to log on windows after failed install of Java

Let's go back to time.I have Windows XP(it's my secondary computer) and I decided to do a restore to my computer,delete everything and reinstall windows.After that,I disabled Windows Update for others reasons( Making computer MUCH slower).I don't think that was important...But ok...Then I installed Windows Service Pack 3(I had WSP2).Knowing that my computer won't install most programs without WSP3.At the last page of the WSP3(The Finish page telling I installed it succesfully),it said I must restart the computer.I accidently clicked restart later and clicked finish.After that,I forgot about restarting after surfing through the internet.Then I wanted to download Java for Minecraft.When installing Java took so long,I found out I hadn't restarted my computer,so I Shut the installation the hard way(through task manager).I restarted my computer and then I as I clicked the wizard,it said "Java is already installed,do you want to reinstall?".It was installed because it said on control panel,so I assumed I am done with Java's installation.The next time I turned on the computer,it was just staying at the background before the "choose user window" but after "starting windows".What should I do?
Thanks

Look at the links at the bottom where my signature is; and click on the one that says system restore and follow the steps in that article. It will show you how to do a restore step by step. Actually; Here is the link to make it easier

System Restore

follow the steps in the above link and hopefully in the end you will be up and running again.