My PC wont post then after resetting cmos its running again ,until a reboot.

[malfunction]

I meant have you stress tested it after booting into OS (Windows, presumably), as in "while it's working" e.g. Prime 95, Intel Burn Test or whatever 'the kids' are using these days (I'm still using Prime 95). That and memtest would help rule out whether this is just a BIOS glitch of some kind or whether something's on the way out. If you want to try and max out your PSU run something like Prime 95 and Furmark at the same time.

[switchmode]

I'm not sure if this is your problem but I had a PC that would have trouble starting up, lived with it for a while then stopped booting at all. Long story short it was the 5V STB Power, Replaced the PSU all good.
When I opened the old PSU for a look I found the capacitor that was on the 5V STB line had leaked.

5V STB Power is on all the time, even when the PC is powered off, also powers the keyboard and any USB plugged in, so can have a hard life.

The 5V STB Power may be bad and dragging the cmos chip down. Even if you have a new battery causing it to behave strange.

Can't be 100 % sure but I would give that a good look at.