Could the problem be my PS?

My pc runs fine for its every day cores(typing,music,book keeping etc.)but,every time I play a game or run a program that might require my pc to put forth some effort it either locks up, gives me some kind of illeagal operation, crashes to the desktop, or gives me a blue screen of death.
It only has a 250wattPS. since I bought it I’ve added a DVD drive, sound card, video card(it came with onboard audio&video), and 2case fans.
Could the problem be that I need a stronger power supply?

My pc’s Specs:

PCC M830 motherboard
1.3ghz Athlon TB
256mb DDR266
Sound Blaster 16PCI
Geforce2MX400
CDRW
DVD
floppy
On Board NIC
56k Modem