There is a movie (possibly made for t.v.) about a clerk who works for
a scientific company.  The head of the company has started up some
accelerator-type machine, causing time to repeat every day (like
Groundhog day).  This clerk is the only one who remembers what has
happened the previous day.  His love interest is a woman scientist who
works at the company.  He prevents her from being murdered, and
eventually also prevents the accelerator from being activated, so time
can continue.  I saw this on t.v. 3-10 years ago.

I believe I know precisely the movie you're talking about. In fact, I
know two versions of it. One is a short film (25 minutes), and one is
a full-length, made-for-TV one. Both have been shown on television (as
I recall, the short film was on Showtime, and the full-length one was
on Fox). The short film was nominated for an Academy Award. Both films
had screenplays which were based upon a short story called "12:01
P.M." by Richard Lupoff.

Here you'll find information on the shorter version:

Internet Movie Database: 12:01 PM (1990)
http://imdb.com/title/tt0098962/

And here's info on the full-length movie:

Internet Movie Database: 12:01 (1993)
http://imdb.com/title/tt0106188/

A couple of brief plot summaries:

"A research scientist discovers a glitch in a secret project that
causes a mysterious time bounce, making the same day occur again and
again. It's a race against the clock to save the life of the woman he
loves and put an end to the cycle."

Yahoo! Movies: 12:01 (1993)
http://movies.yahoo.com/shop?d=hv&cf=info&id=1800194031

"Barry Thomas is an office slacker with an unrequited crush on Lisa, a
pretty scientist who ends up murdered in a drive-by shooting. The next
day though, he's amazed to see her alive.

Putting the pieces together, Barry realises he's stuck in the 'time
bounce', the effect of an experiment gone horribly wrong which is
causing the day to repeat once the clock hits 12:01 am. And only a
freak accident at the exact moment of reset has given him the ability
to remember previous events.

Barry now has a second chance to save Lisa, but soon finds out that
there's more to her death than meets the eye. With the time bounce out
of control and nefarious forces working against him, Barry wonders if
he'll ever find a way to break out of the loop."

Movie Tome: 12:01
http://www.movietome.com/movietome/servlet/MovieMain/movieid-41297/1201/

As far as I know, the short film has never been issued commercially on
VHS or DVD. The full-length film came out on VHS in 1996, and used
copies are readily available:

Amazon: 12:01 (1993) (VHS)
http://www.amazon.com/exec/obidos/tg/detail/-/6304053614

My Google search strategy:

Google Web Search: "12:01" movie OR film lupoff
://www.google.com/search?hl=en&q=%2212%3A01%22+movie+OR+film+lupoff

I hope this is helpful. If anything is unclear or incomplete, or if
this is not the correct film, please request clarification; I'll be
glad to offer further assistance before you rate my answer.

Best regards,
pinkfreud