If I may add to this useful thread:
On older transformers / android versions, PlayStore is dead after the factory reset, and no cache cleaning, or cold booting, or whatever can make it work. Not even time passing by...

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The only workaround I found (after 2 days searching) is here:
STOCK TF101 - Factory reset, Google Play Sto… | Asus Eee Pad Transformer TF101
which means:
1. Find the .apk file (search: "play store", not "playstore"!!!) using a different device of course, as stock browser probably doesn't work either.
2. Copy it via sd card to the TF and run it.
3. Allow installation of Non-Market apps at the message that appears, or through the Settings \ Security.
Everything else gets updated automatically from there-on.
Hope it helped.