Help to determine the weakest link PC

Good evening, forum PG. Already a year probably, maybe more, as I faced quite a common problem — the FPS drop in many games.
Forget riddles, arguments, Tarot cards and dancing with a tambourine, and go straight to the point:

The system unit bought in 2015 , its very build 2013\2014. At the time of purchase, he was distinguished only by the amount of RAM, which was only 4GB and the lack of a DVD drive, which I later unscrewed from the old PC and pasted in the new. At the moment, the characteristics and composition of the PC as follows:
1. CPU: Intel Pentium G3450 3.40 GHz | 2xCore | 2xThreads | Socket LGA 1150 | Model C
2. RAM: 1)Patriot Memory DDR3 1600MHz 4GB. 2)Crucial Technology 4GB DDR3 1600MHz. Total volume: 8GB
3. Video card: NVIDIA GeForce GT 730 | DDR3 | 2GB | Revision A1.
4. Motherboard: MSI H81M-P33 (MS-7817) | 1.0 | PCI Express x16 | BIOS v1.9(Date 03/30/2015)
4. The monitor is on the window of 1280x1024 75MHz, and are now standing on the TV instead of the monitor settings 1360x768 60MHz.
5. Hard drive: WDC WD5000AAKX-60U6AA0 ATA Device 500GB
6. External drive: WD My Passport 0822 USB Device 1TB

Now a little back to the problem. Even taking the old game into your own hands, you will notice that even in the same CoD:WW, CS:Source, CS:GO, WoT, Crysis 2 or Far Cry 3, the FPS does not rise above 20-30, everything else and the camera twitches and jerks(Here it is, the FPS in the case, as they say).
Now about the measures taken:
1. Have peremabiri system unit from scratch, cleaned all that is possible(Unless only not dismantled and was not cleaned inside hard drive :D ).
2. Tried to overclock to increase FPS
3. Twisted, the spit, swore at these settings the NVIDIA — Vert.sync, shaders, antialiasing, filtering, etc, etc
4. Defragmentarea were all 2 disc — external and internal.
5. Updated all the drivers.
6. Re-installed Windows on license clean Windows 7 64bit, with full formatting of the system drive, which eliminates the presence of viruses interfere with the normal functioning of the PC.
7. Changed the monitors, resolve them.
8. In the BIOS, experimented with the frequency settings, put everything to the maximum, the minimum, optimum(is on maximum).
9. In recent times, but rather 3 days ago, changed the thermal grease, which eliminates the throttle as the video card, and CPU.
10. Included in the BIOS OC Genie.
11. Jump with a tambourine around a PC.

What else may be tried with grief, I can't remember. Waiting for your answers and opinions that it can be reliable to find in the system dead link.