BibTeX cannot find .bib file

BibTeX cannot find .bib file

I am using TeXworks version 0.4.5 with MiKTeX 2.9 64-bit on Windows 7.
When I try to typeset the code
\documentclass{amsart}
\begin{document}
Blah blah \cite{grimm}
\bibliographystyle{plain}
\bibliography{diss}
\end{document}
Latex warns that there were undefined references, and in the pdf there is
a bolded question mark instead of the reference, and the references
section at the end is empty. When I run BibTeX by itself I get the error
"I couldn't open the database file diss.bib"
diss.bib looks like this
@article{grimm,
title= "A theorem about random fields"
}
Things I have tried which haven't worked:
Saving the .bib file in the same place as the .tex file
Savind the file in a TDS-compliant root directory
C:\tex-biblio\bibtex\bib\mybiblios\diss.bib and adding this as a root
directory in MiKTeX (it accepts it as a new root directory, but BibTeX
still can't find the .bib file)
Creating a BIBINPUTS environmental variable and adding a path to where the
.bib file is saved
Writing a path to the .bib file when defining which bibliography to use:
\bibliography{C:/Users/Sacrebleurgh/Documents/Latex/diss} - i've also
tried diss.bib.
I originally downloaded MiKTeX with LyX so I tried uninstalling them both
and then installing MiKTeX by itself, but the problem persisted.
Any suggestion as to what might be wrong or other things to try would be
greatly appreciated.