Hi patrick23,
1. Have you made any recent changes on the computer?
2. What is the error message on the blue screen?
3. When does the computer perform slowly?
Refer the below Microsoft article and check if it’s helpful.
Error message when you start a Windows Vista-based computer on which Windows ReadyBoost is running: "STOP: 0x0000006F SESSION3 INITIALIZATION FAILED"
http://support.microsoft.com/kb/939008
For the slow performance of the computer I would suggest that you perform clean boot procedure and check.
There is a possibility that some third party programs installed on the computer is causing the issue.
To help troubleshoot error messages and other issues, you can start Windows Vista by using a minimal set of drivers and startup programs. This kind of startup is known as a "clean boot." A clean boot helps eliminate software conflicts.
Refer the below link to know more about clean boot procedure.
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7
http://support.microsoft.com/kb/929135
Reset the computer to start as usual
After you have finished troubleshooting, follow these steps to reset the computer to start as usual:
a) Click Start, type msconfig in the Start Search box, and then press ENTER.
b) If you are prompted for an administrator password or for confirmation, type your password, or click Continue.
c) On the General tab, click the Normal Startup option, and then click OK.
d) When you are prompted to restart the computer, click Restart.
Hope this helps!
Halima S - Microsoft Support.
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