I have a 2003 Dell Inspiron 5100 laptop -- used for company legacy apps. It's always on (and has been for 16 years!!). Pretty much trouble free. Except, over the past two years, in the rare case that it needed to be re-booted, I can't get it power on for about 20 min or so.
I press PWR button and the LEDs come on, and fan spins ... but screen remains black. Sometimes it shuts down automatically (after 10 sec or so) ... or I shut it down because fan spin is maxed.
It acts like a memory issue. But I have several new (spare) memory sticks ... same issue. A while back, I could get it to immediately re-power more frequently if I used 256MB instead of 512MB memory stick. Now, even the 256MB causes delay.
I was thinking dry electro caps. But I saw pics of the main board and I saw only few electro caps?
FYI: I do use a newer SSD in this Dell. I replaced the 16-yr-old Hitachi 40GB only a few weeks back (it still works perfectly!)
When the laptop is on, it works perfectly. No blue screens, no lock ups. It's a great computer except for the recent delay pwr-up issue.