Yes, Windows XP is installed on the laptop. However, depending on the brand of computer, you will get a System Restore CD or Windows Reinstallation CD. Sometimes the Windows installation files are placed on a hidden partition of the hard drive and the restore CD (like with old Compaqs) contains no OS files, but rather simply directs the install process to that hidden partition.
With some types of OS maintenance, it is vital to have the disk in the drive.
With that said, what brand of laptop do you have?
To obtain replacement disks, see Microsoft article
326246 for contact information and options. You can also contact your laptop manufacturer for replacement disks. There is a nominal fee.
Regarding System File Checker, you should try to run it and see if it prompts you for the disk.
Regarding Java, you can download the most current version
here.
Here are some other things you can do that do not require the Windows CD.
1. Clear all temporary internet files. Open Internet Explorer, Tools menu, Internet Options. Click Delete Cookie, then Delete Files (be sure to check Offline Files). Also Clear History.
2. Clear other temporary files. Open My Computer, right click over Local Disk C:, Properties, Disk Cleanup (on the General tab). You can also download a freeware program called CCleaner
here. I've been using it for several weeks based on recommendations at G2G, and I have had very good results with it. It clears unnecessary files as well as registry entries (it prompts you to backup the entries it removes - so no worries).
3. Defrag C:\. Open My Computer, right click on Local Disk C:, Properties, Tools, Defragment Now.
4. Run Chkdsk. Open My Computer, right click on Local Disk C:, Properties, Tools, Error Checking/Check Now. Be sure to tick both option boxes. You'll be notified that it will run on the next reboot. It should take between 20-40 minutes to run.
5. Check Microsoft Update site for updates for your system.