avrdude error

I recently bought my first microcontroller, it is an arduino clone with atmega8l-bpu.
I just started from the basics.

It worked properly,but it is now giving an error when any program is loaded on it ,
The same error is displayed in the black box whenever I upload a program(like the blink program from the list):

Binary sketch size: 826 bytes (of a 7168 byte maximum)

avrdude: verification error, first mismatch at byte 0x0000
0x3f != 0x00
avrdude: verification error; content mismatch

I tried resetting it manually, but the problem persists.
Please guide me through this problem.
Any assistance will be appreciated.
Thanks,
Shubhang Sharma.