I think your card is quite old and my best guess is it runs out of VRAM when the picture editor opens, which is the first thing that happens when you insert/double click a sprite, tiled background etc.
Could you open a template and hit F7? It should show a VRAM report, something like:
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VRAM usage
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VRAM usage by Construct:
8.34mb textures
15.01mb targets
23.35mb total
Approx 707 MB texture memory remaining
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OK
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(I think the texture memory approxomation might not be in 0.94.3)
I've had other reports of people running out of video memory on 64MB cards, but I can't work out why - the textures used by Construct should only add up to a few tens of megabytes.
Also, it would be useful to know your screen resolution. It's possible turning down your resolution (eg. from 1024x768 down to 800x600) could help.