Veriton N4620G lately takes about 10-15 MINUTES to boot.

GaryRos

When the  power button is pressed it makes 3 short beeps and immediately another 3 short beeps then fan stops, and it tries to boot in 4 seconds again and it beeps 3+3 again, and so on for 10-15 minutes until finally it boots and works with no any problem.
I already tried to replace RAM card, didn't help, 

JackE

The BIOS beep error codes listed are shown below. Since none matches your description exactly but the machine eventually boots, I'm gonna guess the BIOS coin battery has crapped out and needs to be replaced on the mainboard also shown below. Jack E/NJ

GaryRos

id the CMOS battery is used just to save the date/time 

JackE

CMOS battery saves configuration info/data for HDD and a few other pieces of hardware. Jack E/NJ

GaryRos

Thanks a lot for the answer. I may try to replace it. I measured its voltage, it is a little less than 3v. The comp is about 4 years old.  .  BTW, I rebooted the comp today, it took about 1.5 hours of beeping, but eventually it rebooted and works fine.  
All Bios codes can be found in http://www.bioscentral.com/beepcodes/amibeep.htm
3 beeps are RAM failure and I already replaced it, 6 beeps is Gate A20 failure, will look into keyboard controller as well

GaryRos

Changed the CMOS battery, no change, finally rebooted after about 1.5 hours of 3+3 beeps.
When it boots, works perfectly

JackE

Don't just disable but uninstall any non-Microsoft anti-virus or anti-malware you have on the machine. Jack E/NJ

GaryRos

Never have one installed. The Windows Defender it is all I use.
It's unlikely the anti-virus software is involved, the OS has not been even started yet, it is in BIOS

JackE

How about just entering the BIOS menu, press F9 to load defaults, F10 to save settings and exit? Something smells rotten in there somewhere. Maybe the HDD has an issue? Corrupted files? How about scanning it? Jack E/NJ