As we told you on C++ Programming... put the data file in the same folder as your executable file.
Then all you need is the filename, you can get rid of the path entirely...
As in...
fopen("reamaze.dat","r");
We also explained about checking return values to be sure the file is opening...
FILE *fp;
fp = fopen("reamaze.dat","r");
if (! fp)
{ printf("The file did not open");
return 1; }
Also we told you about the change in windows settings to unhide your file extensions...
Control Panel -> Folder Options -> View -> Uncheck "Hide extensions of known file types".
Turn that off and leave it off.
It is very likely your file isn't named simply "reamaze"... it's probably "reamaze.txt" or something similar.
Finally, we told you repeatedly to look stuff up in the Pelles C help files... it's a total documentation of almost everything about Pelles C and it's standard libraries.