Diagnostic software may be helpful.
However, it is also important that you update your post with full system hardware specs and OS information.
Include PSU: make, model, wattage, age, condition (original to build, new, refurbished, used)?
Disk drive(s): make, model, capacity, how full?
Also you can use Reliability History/Monitor and Event Viewer to look for error codes, warnings, or even informational events regarding system performance and problems.
Especially if you can identify any that are being logged just before or at the time of the blinks.
More information needed.
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That said, the blinking could simply be a loose card or connector.
Power down, unplug, open the case.
Clean out dust and debris.
Verify by sight and feel that all cards, connectors, RAM, jumpers, and case connections are fully and firmly in place.