2000 Buick Regal power steering pump was whining for couple of days. When I put fluid in finally, I accidentally started it up with the cap off well then my car started to make a knocking noise and I

SOURCE: Power Steering pump appears to be leaking but is full????

Just guessing. Could it be a warped brake disk? That would cause vibration. And vibration in steering might conceivably cause splashing out the power steering reservoir. You would know if the disk were warped by a shudder when you brake at hight speeds.

SOURCE: Power Steering Fluid???

The power steering pump is located under the alternator near the firewall. It is hard to get to so you most likely need a funnel with a flex pipe to reach it without making a huge mess. I hope this is helpful.

SOURCE: lost owner manual for 92 Buick Regal custom-power steering fluid

The reservoir should be located under the hood on the passenger side, above serpentine belt. Guide your eyes backwards towards the mid section of the engine on the passenger side. the small reservoir will have a small turn cap on top. (passenger side off vehicle)

SOURCE: 93 Buick Lesabre custom 3.8 L with engine knock and stalling

if you can turn the serpentine belt either direction by hand at all you probably need a harmonic balancer..or just look in the passenger wheelwell at the h/balencer and see if the rubber is cracked all the way around.. just fixed one with that issue

SOURCE: 2000 buick regal lse 3.8 wont start or turn over

several things to check out:

get it started and go have the battery, alternator, and voltage regulator tested. No charge at most parts stores.

IF they all test ok then you will need to remove the starter and have it tested. The solenoid could be bad. Was it wet outside the day it wouldnt start? if so then oisture is probably getting into the solenoid.