Free Diagnostic Tool For Memory Leak?

My older online computer, which I recently cleaned thoroughly with the help of MajorGeeks (see my thread 'Need To "clean House". What Do I Do?') runs slower and slower until I reboot it. Then it runs fine at first, but then its speed again quickly degrades. I suspect a memory leak. Would anyone be able to recommend a good diagnostic tool I can download for free to check this out?

System:
Processor: Pentium 4 1.80 GHz
RAM: 1.25 GB
System type: 32-bit

Windows edition:
Windows XP Professional
Version: 2002
Service Pack 3

Browser:
Interner Explorer 8
Version: 8.0.6001.18702
Update versions: 0

 

Memtest86 Free Edition is a specialized tool for checking RAM.
http://www.majorgeeks.com/files/details/memtest86.html

 

Thanks for the recommendation, Tim, and sorry for the slow response, I AM considering Wise Care 365, but right now I'm putting out a fire here, so I'll get to that a little later.

 

Thanks, Eldon, but as you're probably already aware. we'll probably be talking over here first before I get back to this.

 

Every time I have seen this issue on Windows XP it was caused by a memory leak in one of the svchost.exe processes. It is a common known problem on XP that almost always is caused by Windows Update. Click Start, Run, type services.msc, find the service labeled Automatic Updates, right click on it and select stop. If your computer speeds up you will know that is the culprit. There is a hotfix for it. Check out this KB article from Microsoft. https://support.microsoft.com/en-us/kb/916089

 

Thanks Brandon, I've done what you suggested, now let's just see what happens; I'll let you know.