The slow bootup can be due to any of the following reasons:
- Startup items
- Prefetcher information
As you have already tried disabling the startup items, I recommend you remove the prefetch information. I am providing you the detailed information about the prefetcher feature that is available in Windows XP below:
Windows XP Home and Professional monitors the files that are used when the computer starts and when you start applications. By monitoring these files, Windows XP can prefetch them. Prefetching data is the process whereby data that is expected to be requested is read ahead into the cache. Prefetching boot files and applications decreases the time needed to start Windows XP Professional and start applications.
Prefetching is further improved if the files are located next to each other on the outer edge of the disk. Windows XP optimizes the location of boot files and applications when the computer is idle. The optimization occurs in the background. After the initial optimization takes place, subsequent optimization occurs, at most, every three days.
Disable the Windows XP Prefetcher
When troubleshooting either Windows or program start-up issues, it might be helpful to disable the prefetcher, because it runs as a background service while other applications are running or loading.
To disable the prefetcher:
Click Start, Run.
Type regedit and click OK.
Navigate to the following key:
HKEY_LOCAL_MACHINE \ SYSTEM \ CurrentControlSet \ Control \ SessionManager \ Memory Management \ PrefetchParameters
Double-click the "EnablePrefetcher" value.
Change the Value data to 0 to disable the prefetcher.
Close the registry editor and restart the computer.
The EnablePrefetcher Values are:
0 - no prefetch
1 - prefetch applications only
2 - prefetch boot only
3 - prefetch both applications & boot (default)
However, after using XP some time, the prefetch directory can get full of junk and obsolete links in the Prefetch catalog. Removing the files of Prefetch folder will increase the system performance. You can safely remove these files; any files that are needed will be created again automatically.
If still the issue persists, you may need to check for the viruses.