Getting a copy of system.pas isn't going to solve your problem. It sounds like either your install is screwed up or you may have removed the library path from your environment options. Go to the Tools menu and select Environment Options. Click on the Library tab.
You should have four edit boxes, Library path, BPL output directory, DCP output directory and Browsing path.
Click the ellipsis button (...) for the Library path. In the Ordered list of Library paths you should have something like this:
$(DELPHI)\Lib;
$(DELPHI)\Bin;
$(DELPHI)\Imports;
$(DELPHI)\Projects\Bpl;
If you do not, add them.
Your BPL output directory and DCP output directory should both be:
$(DELPHI)\Projects\Bpl
And your browsing path something like:
$(DELPHI)\source\vcl;$(DELPHI)\Source\Rtl;$(DELPHI )\source\rtl\Sys;$(DELPHI)\source\rtl\Win;$(DELPHI )\source\rtl\common;$(DELPHI)\source\Internet;$(DE LPHI)\source\clx;$(DELPHI)\source\websnap;$(DELPHI )\Source\WebMidas;$(DELPHI)\Source\Samples;$(DELPH I)\Source\ToolsAPI;$(DELPHI)\Source\Xml;
(just paste that into the Browsing path edit, then click the ellipsis button).
If that was all set right already then you probably are having problems with the library path. Go look in the delphi directory and see if the lib directory is there and if it contains system.dcu. If not something is very broken and you should probably reinstall.
Grippy has approximately 30,000 hours of Delphi coding experience. srsly.