quite puzzling issue cant upload my code

Ok so here is how the story goes,I bought a arduino mega r3 clone from vendor nearby as soon as I bought it flashed with led blinking program so all well!!

Now,as I require watchdog timer in my project the previous bootloader had a bug where the board will never come out of watchdog reset ,so using USB ISP blanked the chip and flashed it stk500boot_v2_mega2560 all well done led at pin 13 blinking !!

Next step when I tried to upload the code using Arduino IDE stk500v2_ReceiveMessage(): timeout, stk500v2_getsync(): timeout communicating with programmer.Thing to note the RX,TX on the atmega 16u2 doesnt blink ,no serial data coming out whhhhat before it was ok I have not touched the atmega 16U2

So time to debug: 1]bootloader corrupt Solution: Flashed the bootloader again the same thing 2]Under device manager my arduino mega was listed as same COM port as in the arduino IDE COM1 3]So only culprit I guess must be atmega 16U2 soultion:I tried to program it using USB ISP by interfacing with icsp near USB socket but it gives me chip enable error I have one arduino mega with the same bootloader loaded using this since 1 year with no issues

Guys any suggestion to what might be wrong frustrated wtih this issue

One update guys on the arduino mega thats working fine the one I have used for one year ,I can read signature of the atmega 16U2 so the atmega 16U2 of this new board got damage I dont know why :( :(

I do not understand your problem. If you reflash the chip, you have blink which works.

I get the feeling that when you upload your watchdog modified program, then things go bad.

Can you upload a modified version of blink with slower flash?