Would a blown gasket on the turbo of my Volvo S40 T4 1998 be responsible for a total loss of power and white smoke? Where is the turbo located??

Does the smoke smell like burnt antifreeze or motor oil?

A worn turbo or broken would create smoke. Blue or Gray smoke is either worn rings or a clogged PCV. White smoke is from foreign fluid entering the engine. Typically indicative of a head gasket leak. Black smoke is Leaking injectors or an ignition problem or an issue with the turbo.
If you are experiencing a loss in power then you most likely have a worn turbo bearing.

Actually is sounds more like a blown head gasket or intake gasket. The white smoke is probably water.. and my guess is your coolant reservoir tank is dry or soon will be.. and the next thing will be overheating. The water is getting into the combustion cycle and turning to steam as it blows out the exhaust. Hence white "smoke"..

The loss of compression due to the gasket leak on one or more cylinders would account for the loss of power as well.

I was not aware this model came with turbocharger.. unless an aftermarket one was added.

A good shop will do a compression check and identify if it's the head or intake gasket.

Best of luck!

white smoke + adding water with no leaks = blown head gasket

turbo¿¿

check intercooler pipes for splits or holes dont think turbo is at fault you must check pipes carefully remove if you have to to check

Water in combustion chamber makes white smoke--suspect that the head gasket is leaking water into the chamber. If oil leaking around turbo, it may have a bad bearing and bad oil seal. Check waste gate valve and control.

think you may have blown your head gasket ( turbo pushing too much boost)

check to make sure the turbo oil return pipe is not clogged. if it is pressure will build up causing oil leak through seal causing it to smoke.

if its white smoke you have a blown head gasket.