Black monitor screen

You may have loaded software that is using too many resources and slowing the start of the computer, you can try system restore, which sets the drive back to an earlier time, before the problem started.
This does not always work, but it may be one of the simplest ways to fix a problem...

You may have accumulated malicious software or downloaded something that corrupted your system...
update antivirus and scan entire computer...
perform repair install of operating system, using directions posted in this forum, sixth post from the top.

Does the BIOS screen show up? Or is it just black and then you see Windows loading? 2-3 minutes is not a terrible boot time, especially for a system a few years old. Sometimes drive issues can cause this as the drive seeks around for the files or checked bad areas. Do a checkdisk, see if that will help.