I have a lot of experience with the M73s SFF and mini towers. Junk. Sell it if you plan on gaming...it was designed as a very budget oriented office use option...not a gaming PC.
Their MBs are crap....the worst thing is data storage/memory performance is atrocious. Even with an SSD it is disappointing...but better than an HDD obviously.
We sell a lot of M73s for budget office users...but even the builds I do around the same price run circles around the Lenovos. Being a distributor and seller for their products we even compared the old M72 to the M73 and the M73s performance was slower both in measured tests between startup, data transfer and benchmarks and in just general use A/B comparisons.
If you must use it for gaming....on that SFF you need a half height card... And odds are that card will not be a potent gaming card. That PSU can handle CAD cards with ease though. But again...overall system performance is quite disappointing.
Sell it, buy used Haswell parts is a standard case and be much happier.
I used to build Biostar B85S3+ + Pentium G3220 (or i3/5/7) + HDD/SSD with an EVGA 550w PSU in a Cooler Master N200...and that Pentium build would dominate an i3 M73 all day long in everything. We had demos go out to several customers, my bosses were in disbelief until we did a side-by-side on the bench. Needless to say if you can still pick up a Biostar B85S3+ on Newegg for $58 USD...its worth every penny for a solid budget Haswell build.
If you insist on wasting time and money repurposing that M73 for a use it was never designed or intended...get a better PSU...cut a hole in the lid and use a full height 750 ti. Don't expect your benchmark or FPS results to match what you read about others achieving with i3s and GTX 750s though. M73s are crippled budget junk that's a glorified spreadsheet editor at best...web browser for cloud based work sources by design.
