Dead sourdough

Hi all,

I'm new to forum but not that new to baking sourdough bread. I baked very often till i was heavily pregnant with my scond child and had over a year break. We moved houses during that time. Recently decided I'dm like to go back to baking my own bread. Prepared the mix and it started growing, had nice smell and on day 3 it collapsed. Was hoping i could save it but it got mouldy (badly!!) so i dumped and made new one and it grew nicely. so as usually put it away to the fridge and when i took it out to liven it up before baking, it had no bubbles nor it got any after the feed:( after 3 days of nothing happening i dumped it and now im puzzled. no idea what went wrong. twice in a row.never ever happened to me before and i stored sourdough in different places with different temperatures. any idea on how to avoid it? im dying to make some more sourdough bread:((

Thanks in advance!