Give memtest86+ some time alone with your computer after it begins. After a single successful batch of tests, known as a pass, you'll see the message "Pass complete, no errors, press Esc to exit." You can exit memtest86+ after the message appears or allow it to perform multiple passes. If you see an error, you likely need to replace one or more of the RAM sticks in your PC.
But wait, there's more!
Even though you're not installing it on your hard drive, that itty-bitty Ubuntu live drive is a full Linux system, so there's a lot you can do with it. Even if you boot it on a computer infected with a petri dish of Windows malware, it will be secure and isolated from any problems with the Windows software. PCWorld's Ubuntu guide for displaced Windows users has much more background information if you want to learn more about the operating system's ins and outs.
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