Abs problems

I have a 1990 Oldsmobile Toronado Trofeo. I got in it the other day and started it and put it in gear. I noticed the brake pedal was hard as a rock, and my abs and brake stayed on in the instrument cluster. It usually goes off after a few seconds after starting the car. This car has a on board diagnostics system . I ran threw it and it didn?t show any codes. I pulled out the shop manual and it also didn?t show anything about what I am experiencing. I pulled that would disable the abs also the abs module in the trunk still nothing the pedal was still solid. Under the hood by the master cylinder were 4 connectors I unplugged them one at a time to see if that would do something and yet again nothing.

So my next though was lets see if I can bleed the pressure off so I did the front 2 brakes first. As soon as I opened the valve they went to the floor. Ok so I went to the back brakes did the same nothing came out any air or brake fluid. My first thought was the paportion valve is bad or stuck. By this time I have been working on this for about 4 or so hrs and I stopped where I was so I could do some reading up on it later. The car sat there for about 2 hrs then I had to move it to put my other car in the car port I got in and

Put it in gear and the brakes we back to normal. Abs brake lights went off and all drove the car around the block a few times everything seems fine. I didn?t get under the car and see if I was getting fluid to the back calipers but the stopping power seemed even. So I just assumed it was working fine? Now the car has been sitting a week I haven?t drove it

Kind of in fear of not really knowing what happened to cause that. Couldn?t have been a stuck valve in the back? Anyone has this happen before. Any feedback is appreciated.