Nissan Sentera 2005 Help Needed
 

I started my car alright this morning after a heavy rain last night(car was parked outside last night), drove for about 5 km, went to the bank and when started again afterwards, although it started alright but I had no power(pushed the accelerator but the engine didn't respond). Then I turned on the AC, pushed the gas and I had power come on for a second and died immidiately. This was happening frequently.
At first the battery warning sign was on but later the brake warning sign[!] also came on and stayed on. Also the sign saying "service the engine soon" has been on for almost 2 years.
I checked the belts. They are tight and alright. The battery connections are tight and no problem with them. This is my very first issue with this car after 4 years of driving it.
Any idea/tips?