What's the best way to connect a PC (with DJ software) to a Fender PAssport 500 PRO (I want stereo input)?

You can get it here: https://support.fender.com/hc/en-us/article_attachments/207323343/Passport_500_Pro_manual.pdf

If this system is still under warranty get it to a warranty service center. This is an early stage symptom of failure with the Power Amp IC. Fender has a good warranty policy on this stuff - 1 to 3 years

If not under warranty you may want to wait until it the problem is more persistent - easier for a tech to fix - unless it IS every time right now. A good tech can identify the issue quickly once "on the bench". My 'gut' feeling is the Power Amp IC when the system is first energizing to full stable power.

Fender Passports are notorious for being badly built with poor reliabilty. Trade it in for a fiver and buy something of better quality.

You are in danger of popping the amp. The Fender passport 150 would be capable of covering about only a 20 foot by 20 foot area. If your area is bigger than that, you need more power and certainly bigger speakers. I would NOT recommend the larger Passport systems as the speakers are too directive for what sounds like your use... also there are reliability issues.

you can use the line in/mic stereo input, but you will have to turn the input level way down to around 1 or 2.

i assume that the record outputd a re rca outs. you can get a rca stereo to 1/8 inch stereo adapter, like the ones they use to connect protable cd palyers to recievers, and then get a 1/8 inch stereo to 1/4 inch stereo adapter form radio shack to complete the connection.

Unless you abused the cable badly, this is UNLIKELY. More probable is failure of the amplifier.
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'The Speakon connectors are usually pretty reliable,

Since the mixer has a line level output, yes you can use a home stereo for the "AMP". Use the AUX IN, TAPE IN or CD IN on the stereo and connect the speakers as you normally would.

Dan

Plug your keyboard into a line input. Run a cable from the stereo out put jack into a separate amplifier with a speaker e.g. a self contained powered monitor.

Run out of the stereo output jacks into a separate amplifier and speakers. The amplifier send jack only sends signal from the particular channel it is part of. In other words to get all the signals from all the channels you would need another mixer, amp and speakers. It is easier to use the stereo out which will give you all the signals. If you only use left out or right out make note of where your panpot is set for each channel.

It seems like the speaker jack tip needs cleaning, or the contact has become bent away from the connector and needs to be re-aligned.  The Passport is a portable system, so after years of plugging and unplugging the speaker jacks may be worn.  Try using the "Stereo 2" connectors. You can also try cleaning the jack with electrical contact cleaner, and. a cotton swab.