There is a PRTSC button, but it hasn't done anything atm.
I am assuming that you use Windows XP or later.
Ignore SYSRQ, it is almost redundant.
Your PRTSC button should work; maybe I wasn't clear enough.
1 Maximize the page you want to capture.
2 Hit PRTSC
3 Open MS Paint
4 Assuming that PRTSC has worked you should see that the "Paste" command in the MS Paint Toolbar is black text (rather than grey). (Depending on the version of MS Paint, you may need to look for the "Paste" command under the "Edit" menu if you still use XP.) If it is black text, then when you select "Paste" it should paste the captured screen shot into MS Paint. If the "Paste" command is written in grey, then either you did something wrong, or the button is not working.
BTW, SYSRQ means System REQUEST, not REQUIRED. In the "days of old" it was used to interrupt current processing to send commands to the operating system. I have not seen any use for it in many years.