Pc goes to stand by mode while playing bf2042

41 is a power issue but might not necessarily be the PSU. As a quick run through of some of the likely offenders: 
1. In terms of power supply most people overestimate, anything 500-650W is fine for 99% of rigs. I'd be more wary if this is a new PSU that isn't from a reputable vendor (NEVER get an off-brand PSU) or if you got a seemingly good deal for like a "platinum" or "diamond" rated PSU, the real reputable vendors typically sell affordable units at bronze/silver/gold. If it's one of these from a name brand, wouldn't be my first thought. PSUs can age out, technically after 5 years or so but realistically I wouldn't expect it under 7-10. 

2. Have you recently added any RAM? For a quick cheat sheet: every stick should be the same make, capacity and speed. (no 16+32, no 3200+3600, no patriot+kingston). If you have 4 or more slots and aren't using each, ensure your sticks are allocated in the correct locations (i.e. for 2 sticks on a 4 slot, most boards serialize 1 and 3 not 1 and 2). 

3. Do you have XMP/fast boot enabled? If so, try turning them off and seeing if the issue persists. Also, if you've never updated your board, it's worth checking your board's patch notes to see if there's a BIOS update needed to support XMP profiles of certain speeds/makes. (NOTE: BIOS UPDATES are risky and can brick your board, don't do it unless you see specific need to and have backups).

4. If you haven't yet, check for chipset drivers and graphics card updates. A clean install for your graphics card would probably be a good move. 

5. Also do the image/SFC steps I outlined above. 

6. Download monitoring tools and benchmarking software and check if your temps are getting too high and if so, where. 

7. If all else looks good, I'd consider whether the actual power supply from the wall is OK. I've seen some bad power strips or outlets give me grief and it'd only show up on resource intensive games like TWWH3. 

TL;DR 41 is "I lost power and I don't know why".